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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。
You become immune to a disease or a drug, as in the above examples, but immune from something when the object is some kind of obligation or duty, such as taxation, or something that can happen to you, such as prosecution.
另外整个that从句用的是虚拟语气，所以动词都要用虚拟形式。排除C和A。
虚拟语气：主将从现。 If they were XXX, they would XXX
immune to
which caused
都是过去时
eg： A wildlife expert predicts that the reintroduction will fail if the density of the timber wolf population in that region is greater than one wolf for every 39 square miles.
考察：
句意， 虚拟语气
if 条件从句的谓语动词用虚拟语气were，主句也要用虚拟语气
if I were you, I would/should be....
题中if条件从句用了if，主句后面要用would/should do虚拟语气来表示
if虚拟也可以表示推测：predict /expect that whether significant warming will occur and what impact it would have if it did
2. immune to是免疫某种细菌or疾病，而immune from是逃脱某种duty or fee