关于estimate的用法？

Paleontologists believe that fragments of a primate jawbone unearthed in Burma and estimated at 40 to 44 million years old provide evidence of a crucial step along the evolutionary path that led to human beings. Dfficeffice" />

(A) at 40 to 44 million years old provide evidence of

(B) as being 40 to 44 million years old provides evidence of

(C) that it is 40 to 44 million years old provides evidence of what was

(D) to be 40 to 44 million years old provide evidence of

(E) as 40 to 44 million years old provides evidence of what was

答案是D，我选对了。但是我不太清楚在什么情况下用estimate...at,什么情况下用estimate to be....？有人能帮忙解释一下吗？

谢谢了。

Estimatefficeffice" />

Verb

GRE/GMAT/LSAT CR, RC

Estimate that…

Estimate sth

The projected total of corporate contracts with minority businesses for the early 1980’s is estimated to be over 53 billion per year with no letup anticipated in the next decade.

a lizard was recently found that is estimated to be 340 million years old.

M-W

ESTIMATE implies a judgment, considered or casual, that precedes or takes the place of actual measuring or counting or testing out **estimated the crowd at two hundred**.

是否可以说estimate to be+时间；estimate at+数量?

Estimate还可以作名词