请问两题XDF语法分册的题目（找不到大全对应的题号），拜托了！

mercuryfeng

这两题都想了好久都想不明白，请大家看看，谢谢！

第一题是section 10的第14题，p121.

scientists have dated sharp-edged flakes of stone found in the fine-grained sediments of a dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60 million years ago,pushing back by more than 150,000 years the earliest date when it is known that humans made stone tools.

A.when it is known that humans made

B.at which it is known that humans had made

C.at which humans are known to have made

D.that humans are known to be making

E.of humans who were known to make

这题的答案是E,想不通啊！of humans是什么用法？还有为什么用时态were？

第二题是section11的第1题 p123

Although dozens of New York's small museums are either devoted to local history or various ethnic groups,there are many one -of-a-kind museums from Manhattan to the Bronx that are open for exploration on summer weekends.

A.Ahthough dozens of New York's small museums are either devoted to local history or various ethnic groups,there are

B.Although dozens of New York's small museums are devoted to local history or various ethnic groups

C.Dozens of New York's small museums are devoted to local history or various ethnic groups,but there are

D.Dozens of New York's small museums are devoted to local history or various ethnic groups, and there are also

E.Devoted to local history or various ethnic groups,dozens of New York's small museums and also

这题压根没有搞懂是什么意思！能麻烦大家讲一讲吗？谢谢哦！

joe11

第一题 = 天山-7-41  Answer:Ｃ

第二题　＝　大全－７８