作者：英吉
Most vaccines are derived from weakened or killed strains of the same virus that they prevent, unlike the derivation of smallpox vaccine from a different virus altogether.
(A) the derivation of smallpox vaccine from a different virus altogether
(B) smallpox vaccine, which is derived from a different virus altogether
(C) smallpox's vaccine, which gets derived from a different virus altogether
(D) when smallpox vaccine is derived from an altogether different virus
the altogether different virus from which smallpox vaccine is derived
原文大致意思：大概就是说两种东西的起源不一样
题目分析：原文有一个类比，就是most vaccines的起源和smallpox的起源进行的对比，A说的是 the derivation of smallpox vaccine而前面说的是most vaccines，两者之间不能进行对比，杀！
B后面说smallpox vaccine前面说most vaccines可以进行对比，留着。
C说most vaccines后面说smallpox’s vaccine，人家强调的是天花疫苗，不是天花的疫苗，没有必要加’s，干掉。
D加了when和前面的most vaccines无法进行对比，干掉。
E说 the altogether different virus也无法和前面进行对比，杀！
