求救高手时态问题，两道时态题的对比，真的搞不懂啊！～

请教高手一道语法题，关于时态问题

补充题section21-17
Bob Wilber became Sidney Bechet's student and protege when he was nineteen and, for a few years in the 1940's, came as close to being a carbon copy of the jazz virtuoso in performance as anyone has ever come.
(A)as anyone has ever come
(B)as anyone ever had been
(C)as anyone ever had done
(D)that anyone ever did
(E)that anyone ever came

答案是A

补充题079
Opened in 1683,the Ashmolean was the first public museum in Great Britain, while earlier the Bodleian has been the first truly public library.
(A)while earlier the Bodleian has been
(B)where the Bodleian earlier is
(C)just as earlier the Bodleian had been
(D)as the earlier Bodleian has been
(E)the Bodleian earlier being

答案是C

这两题为什么前面一个用完成时，后面一个用过去完成时？究竟怎么判断？答案说前一题没有明确的过去的过去的标志，那么后面一题标志是什么？

tinant mm,

强烈推荐先参考GMAT区域各版块的置顶贴，好东东多多！

先请下载目前市面上最全的GMAT语法复习材料 － 俗称“大全”：
http://forum.chasedream.com/dispbbs.asp?boardID=23&ID=21000&page=1

关于如何与你手中的资料题号对应，请参考：
http://forum.chasedream.com/dispbbs.asp?boardID=23&ID=24247&page=1

若对大全中各题目有任何疑问，可以先参考前辈们的精彩讨论，置顶贴中有如下汇总：

OG提问总结
http://forum.chasedream.com/dispbbs.asp?boardID=23&ID=27472&page=1

885提问总结
http://forum.chasedream.com/dispbbs.asp?boardID=23&ID=27532&page=1

补充题250题
http://forum.chasedream.com/dispbbs.asp?boardID=23&ID=27505&page=1

最新真题22题
http://forum.chasedream.com/dispbbs.asp?boardID=23&ID=59129&page=1

GWD讨论汇总
http://forum.chasedream.com/dispbbs.asp?boardID=23&ID=56794&page=1

备注：GWD不含在“大全”中，完全不懂什么是GWD的可以参考：
http://forum.chasedream.com/dispbbs.asp?boardID=34&ID=58504&page=1

如果前辈们的讨论仍未能解决你的问题，请把原题目顶出来，继续讨论。

若有新题问题，请按照标准方式发帖，即方便大家回复，又方便后人查阅参考。
http://forum.chasedream.com/dispbbs.asp?boardID=23&ID=36320&page=1

谢谢！

祝你复习过程顺利、愉快！