关于estimate to be 和 date at的两道题 求指点

duke182

题1：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.
(A) at 40 to 44 million years old provide evidence of  
(D) to be 40 to 44 million years old provide evidence of (correct)



题2： Rock samples taken from the remains of an asteroid about twice the size of the 6-mile-wide asteroid that eradicated the dinosaurs has been dated to be 3.47 billion years old and thus is evidence of the earliest known asteroid impact on Earth.


(C) have been dated to be 3.47 billion years old and thus are
(E) have been dated at 3.47 billion years old and thus are  (correct)


看了Ron的解释：
题1中 ：[size=15.003px]"estimated at 40 to 44 million years old" is incorrect not because of idiomatic rules, but, rather, simply because "40 to 44 million years old" is not a NOUN.
题2中： [size=14.007px]the only difference between (c) and (e) is idiomatic expression.


请问 这两题不同的地方只是因为estimate at 不是固定搭配吗？