When a disease of epidemic proportions threatens the public, scientists immediately get to work, trying to locate the source of affliction and find ways to combat. Vaccination is one of the effective ways to protect the (1) population of a region or country which may be (2) grave risk. The process of vaccination allows the patient’s body to (3) immunity to the virus or disease so that, if it is encountered, one can fight it (4) naturally. To accomplish this, a small weak or dead (5) of the disease is actually injected into the patient in a controlled environment, (6) his body’s immune system can learn to fight the invader (7) . Information (8) how to penetrate the disease’s defenses is (9) to all elements of the patient’s immune system in a process that occurs naturally, in which genetic information is passed from cell to cell. This makes sure that (10) the patient later come into contact with the real problem, his body is well equipped and trained to (11) with it, having already done so before.
There are, however, dangers (12) in the process. (13) , even the weakened version of the disease contained in the vaccine proves (14) much for the body to handle, resulting in the immune system (15) , and, therefore, the patient’s death. Such is the case of the smallpox vaccine, (16) to eradicate the smallpox epidemic that nearly (17) the whole Native American population and killed massive numbers of settlers. (18) 1 in 10,000 people who receive the vaccine (19) the smallpox disease from the vaccine itself and dies from it. Consequently, the process, which is truly a (20) , may indeed hide some hidden curses.
19（）
A.infects
B.affects
C.effects
D.contracts
参考答案：D
解析：
[注释] 词义搭配。contract在本句中的含义是(=catch or develop\[an illness\])感染(疾病)，例如：contract SARS/a cold/typhoid(感染非典/感冒/伤寒)。contract作主动语态谓语动词用时，其主语是某人。infect vt. (=cause sb./sth. to have a disease)使某人/某物感染。例如：1)Anyone with SARS may infect the people around him．(患非典的人可能会使周围的人感染。)2)The SARS virus infected almost the entire class．(非典病毒感染了几乎全班学生。)从上述二例可以看到，infect意为“(某病源)使某人感染”，而contract意为“(某人)感染得了(某病)”。affect vt. 影响；effect vt. 产生，均不能入选。