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题库 / OG2018-SC-735
The English physician Edward Jenner found that if experimental subjects were deliberately infected with cowpox, which caused only a mild illness, they are immune from smallpox.
which caused only a mild illness, they are immune from
causing only a mild illness, they become immune from
which causes only a mild illness, they are immune to
causing only a mild illness, they became immune from
which caused only a mild illness, they would become immune to
题目分析：
略。
选项分析：
A选项：由于they are immune from smallpox是一个虚拟的情况，即，它是存在于“实验者感染cowpox”的情况下的，因此，其应该用虚拟语气，即，they would become immune from smallpox。
B选项：分词短语causing only a mild illness是伴随状语，其主语为它所修饰的句子的主语，即，experimental subjects。但在逻辑上，引起疾病的应该是 cowpox，而不是experimental subjects。
C选项：本选项错误同选项(A)。
D选项：本选项错误同选项(B)。
E选项：Correct. 本选项在语法和逻辑上均是正确的。
对于D选项，有以下疑问：
1，分词短语causing only a mild illness，可以看做是非限定性定语从句的简化吗？它修饰cowpox
2, 【If A 一般过去式，B+一般过去式】在语法上是否正确？难道一定要用【If A 一般过去式，B+虚拟语气】的结构吗？这里陈述的实验中观察到的事实，if A相当于是一个条件判断，B+一般过去式陈述观察到的结果，这样有错吗？
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