求助sat语法题！！！(Unlike)severaldecadesago,today'slibrariansteachstudentstoevaluatetheaccuracyandobjectivityofonlineresourcesinadditiontohelpingthemfindparticularbooks.A原句BUnlikethemofCUnlikethoseofDCont

Question

求助sat语法题！！！
(Unlike) several decades ago, today's librarians teach students to evaluate the accuracy and objectivity of online resources in addition to helping them find particular books.
A原句
B Unlike them of
C Unlike those of
D Contrary to
E Contrary to those
答案是C
请帮忙解释一下其他几个选项为什么不对。 尤其是B选项 。正确答案的those到底指什么？

Answer 1

contrary 是与什么什么完全相反；unlike 是表示不同于什么什么 

根据整体意思可以判断，应该用 Unlike       

those 指的是 today's librarians  而不是  librarians 所以不用 them

也可以根据字面意思，them是说人，those是说事。今时不同往日，不但说人，更强调的是整个事