[简答题]Many man-made substances are replacing certain natural materials because either the quantity of the natural product can ’not meet our ever-increasing requirement, or, more often, because the physical property of the synthetic substance, which is the common name for man-made materials, has been chosen so that it would be of the greatest use in the fields in which it is to be applied.

[简答题]Many man-made substances are replacing certain natural materials because either the quantity of the natural product can ’not meet our ever-increasing requirement, or, more often, because the physical property of the synthetic substance, which is the common name for man-made materials, has been chosen so that it would be of the greatest use in the fields in which it is to be applied.

[填空题]They were certain that this problem, like so many other________problems, did not ever have to be________, but could be resolved through oblique means.
A. A．insoluble ... solved
B．nettlesome ... faced
C．winsome ... ignored
D．troublesome ... categorized
E．fulsome ... persuaded

[单项选择]

Vitamins are a group of substances found in food. The body needs them for life and health. So naturally, many people are concerned with the question: Am I getting enough vitamins, and am I getting the right kind
Even though very small amounts of each vitamin are enough for the needs of the body, the worry people have about vitamins has some basis. And this has something to do with their diet-- the food they take in. A person eating a good variety of foods gets all the vitamins now known to be needed (with the possible exception of Vitamin D).
The problem is that there are many people who don’t choose foods wisely, don’t get enough variety, and don’t eat the basic foods they need to gettheir vitamins. So the answer to this question is: no extra vitamins are needed, providing you eat proper foods. In fact, many of the vitamins cannot be stored in the body, so when extra vitamins taken
A. they are harmful to your body
B. you get all the vitamins now known to be needed
C. they help our bodies more properly
D. your body simply gets rid of them

[填空题]Snorted substances reach the brain faster than injected substances.

[单项选择] On Antibodies Substances foreign to the body, such as disease-causing bacteria and viruses and other infectious agents, are recognized by the body s immune system as invaders. Our natural defenses against these infectious agents are antibodies, proteins that seek out the antigens (抗原) and help destroy them. Antibodies have two very useful characteristics. First, they are extremely specific; that is, each antibody binds to and attacks one particular antigen. Second, some antibodies, once activated by the occurrence of a disease, continue to confer resistance against that disease. Classic example are the antibodies to the childhood diseases of chickenpox(水痘) and measles. The second characteristic of antibodies makes it possible to develop vaccines. A vaccine (痘苗) is a preparation of killed or weakened bacteria or viruses that, when introduced into the body, stimulates the production of antibodies against the antigens it contains. It is
A. To clone (克隆) themselves
B. To be used therapeutically
C. To be diagnose some diseases
D. To find out whether something foreign is in the blood