（2014年北京市西城区高三5月二模试题）31. A person who has never tasted bitter won’t know ______ sweet is.
A．which
B．what
C．when
D．why
答案：B
本句中的动词know后面是一个宾语从句，这个宾语从句的主语是sweet，系动词is后面缺少了表语。CD两项是连词副词，只能在句中做状语，不能做表语。Which一直都有疑问的意思，表示具体范围之内的“哪一个”。所以使用what，既引导起这个宾语从句，也在宾语从句中做系动词is的表语。故B正确。
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| Have you ever imagined that you could be cloned (克隆) like Dolly,the sheep,in the not too distant future? The news that a human embryo (胚胎) has been 1 cloned for the first time has caused mixed reactions(反应). The 2 was carried out by scientists from the Advanced Cell Technology Inc(ACT),in Massachusetts,US. The group 3 the news on November 25. This is not a cloned human being. "A 4 is alive,it walks,it breathes,"said Jamie Grifo,an expert on the study of cloning at New York University School of Medicine. "This is a set of cells in a lab that will be used to 5 someone's life." Such research could lead to treatment for 6 such as heart disease,AIDS and even cancer, 7 scientists. Despite high hopes from other scientists,the news 8 concerns immediately from religious and political leaders. Several 9 in the US do not allow human cloning. President George W.Bush also made it clear that he is 10 any type of human cloning. However, the 11 at ACT said they have no interest at present in developing an early embryo into 12 . Animals have been cloned repeatedly since Dolly,the sheep, 13 in 1997.And there were no real technical 14 to stand in the way of scientists making a cloned human embryo. This time the research group used traditional cloning technology with a human 15 . 16 it was given DNA from an adult cell,the egg began to 17 . 18 it was stopped from becoming a baby-at a stage in which it was 19 a ball of cells. The 20 technology has been used to clone sheep,cattle and monkeys. | ||||
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