大学英语四级模拟试题（1）_第2页

　　Vitamin D, or calciferol, is another fat soluble steroid vitamin which functions to stimulate calcium uptake from the gut and its deposition in bone. vitamin D acts as a hormone when converted by enzymes in the gut and liver into an active form of "active vitamin D", which stimulates epithelial cells in the intestine to absorb calcium. vitamin D is therefore essential in growing children's diets to enable the growth of strong bones. Without adequate amounts of vitamin D children can develop rickets, which is the deformation of the legs caused when they lack calcium to strengthen the bones. In adults a lack of vitamin D in the diet can lead to osteomalacia, a progressive softening of the bones which can make them highly susceptible to fracture.

　　Vitamin D is made by the body when exposed to sunlight and is stored in the muscles, however, if the skin is rarely exposed to the sunlight or is dark little vitamin D is produced. Foods such as eggs and oily fish are all rich in vitamin D.

　　Vitamins K

　　Vitamin K, phylloquinone, is found in dark green leafy vegetables such as spinach and kale. It is a fat soluble vitamin which is involved in the clotting process of blood. In the intestines bacteria synthesize a number of important clotting factors which need vitamin K. Without vitamin K cuts can fail to heal and internal bleeding can occur.

　　Vitamins C

　　Vitamin C is a water soluble vitamin, known chemically as ascorbic acid. It is found in citrus fruits such as oranges and lemons, and also in potatoes and tomatoes. The main function of vitamin C is the formation of connective tissues such as collagen. It is also known to be an antioxidant which helps to remove toxins and aids the immune system. A lack of vitamin C leads to Scurvy, a condition experienced by sailors on long journeys when they did not have fruit in their diets. Scurvy causes painful, bleeding gums. As vitamin C is water soluble, it is not toxic in high doses as it can be excreted in the urine, very high doses can however cause diarrhea.

Vitamins B

　　B group vitamins have a wide range of roles acting as co-enzymes in metabolic pathways. They are found in most plant and animal tissues involved in metabolism, therefore foods such as liver, yeast and dairy products are all rich in B group vitamins. Deficiency of B group vitamins include dermatitis, fatigue and malformation of red blood cells.

　　1. An adult needs about 12,000kJ of energy a day from ________.

　　A. the cell B. the respiring process of carbohydrates

　　C. fats in the cell D. a balanced diet

　　2. Carbohydrates are ultimately absorbed into cells in the process of _______.

　　A. digestion B. respiration

　　C. oxidization D. mobilization

　　3. The Essential Amino Acids which build part of proteins can be obtained from______.

　　A. stomach B. body tissues

　　C. the body D. the diet

　　4. The ultimate cause of kwashiorkor is lack of ________.

　　A. protein B. carbohydrates

　　C. vitamins D. diet

　　5. Vitamins are called “micronutrients” in that _________.

　　A. excessive fat soluble vitamins can be excreted in the urine B. the body only requires small amount of vitamins

　　C. a dose of 3300mg of vitamins can be considered toxic D. the high concentrations of water soluble vitamins are toxic

　　6. Night blindness is a disease normally caused by lack of __________.

　　A. fat soluble vitamins B. water soluble vitamins

　　C. vitamin A D. innate disability

　　7. The main function of vitamin D is to prevent adults from ________.

　　A. the growth of strong bones B. fracture

　　C. a progressive softening of the bones D. calcium uptake from the gut

　　8. Although the human body produces vitamin D normally, it fails to do so if there is not enough ______________.

　　9. The reason why vitamin C is seen as an antioxidant is that it drives __________ out of the body.

　　10. If you are in lack of B group vitamins, you should turn to _______________.
Part III Listening Comprehension (35 minutes)

　　Section A

　　Directions: In this section, you will hear 8 short conversations and 2 long conversations. At the end of each conversation, one or more questions will be asked about what was said. Both the conversation and the questions will be spoken only once. After each question there will be a pause. During the pause, you must read the four choices marked A), B), C) and D), and decide which is the best answer. Then mark the corresponding letter on Answer Sheet 2 with a single line through the centre.

　　11. A) He thinks he’s very organized.

　　B) He doesn’t want to join the display.

　　C) He doesn’t think he should lead the study group.

　　D) He knows someone who can lead the study group.

　　12. A) He doesn’t know where his brother keeps his computer.

　　B) The woman should buy a used computer.

　　C) He doesn’t know how much computers cost.

　　D) His brother paid too much for the computer.

　　13. A) It’s been to warm to wear the jacket.

　　B) The jacket is too big for him.

　　C) He doesn’t like cold weather.

　　D) He didn’t buy the jacket until cooler weather arrived.

　　14. A) He started the semester in a bad mood.

　　B) He’s not usually bad-tempered.

　　C) He has few responsibilities.

　　D) He doesn’t like the man.

　　15. A) He forgot to cancel the reservation.

　　B) They can go to the restaurant after the woman has finished working.

　　C) He has to work late tonight.

　　D) They don’t have a reservation at the restaurant.

　　16. A) Use bleach on his socks.

　　B) Buy new white socks.

　　C) Wash his red T-shirt again.

　　D) Throw away his pink socks.

　　17. A) He isn’t satisfied with his progress.

　　B) He wants to move up more quickly than he’s presently doing.

　　C) He has advance quickly enough in his career.

　　D) He feels frustrated as he tries to move up the ladder.

　　18. A) Try on a smaller sweater.

　　B) Look for another style at a different store.

　　C) Give the sweater away as a gift.

　　D) Exchange the sweater for a bigger one.

　　Questions 19 to 22 are based on the conversation you have just heard.

　　19. A) She's unable to attend the study session.

　　B) She has seen a doctor recently.

　　C) She's concerned about medical care.

　　D) She mentions the need for some medical tests.

　　20. A) To improve the study skills of university students.

　　B) To suggest changes in the student government.

　　C) To give people the opportunity to speak with a politician.

　　D) To discuss graduation requirements for political science majors.