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  3. Despite the fact that today viruses are known to cause cancer in animals and in certain plants, where exists a great reluctance

Despite the fact that today viruses are known to cause cancer in animals and in certain plants, where exists a great reluctance

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问题     Despite the fact that today viruses are known to cause cancer
in animals and in certain plants, where exists a great reluctance (1)______
to accept viruses as been of importance in human cancer. Basic (2)______
biological phenomena generally does not differ strikingly as (3)______
one goes from one species to other. It should be recognized that (4)______
cancer is a biological problem and not a problem that is unique
for man. Cancer originates when a normal cell suddenly becomes
a cancer cell which multiplies widely and with apparent restraint. (5)______
Cancer cells originate in many different kinds of cell, but the
cancer cell usually continues to carry certain traits of the cell of
origin. The transformation of a normal cell to a cancer cell may (6)______
have more than one kind of cause, but there’s good reason to
consider the relationships exist between viruses and cancer.
    Since there’s no evidence which human cancer, as generally (7)______
experienced, is infectious, many person believe that because (8)______
viruses are infectious agents, they can possibly be of important in (9)______
human cancer. Furthermore, viruses and examples are known in
which a virus never kills its host can mutate to form a new strain (10)______
of virus that always kills its host. It does not seem unreasonable
to assume that an innocuous latent virus might mutate to form a
strain that causes cancer.
选项
答案virus∧never—that
解析 分析句子可知，下一行的that引导的定语从句修饰virus，与后面的a new strain of virus that…相照应，而in which所引导的定语从句的句子主干是a virus…can mutate，故应在本行的virus和never之间加引导词that，引导定语从句never kills its host，来修饰virus。
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