Sentence Correction

the problem is not solved.

in Q 27, og 12, gmat said that "estimated at" is wrong and "estimated to be" is right.

in Q 140, og 12, gmat said that " estimated to be" is wrong and " estimated at" is wrong.

in both questions, the use of "estimated" is similar.

pls, explain, thank you

27. 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
(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

OA IS D.

140. 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.
(A) has been dated to be 3.47 billion years old and
thus is
(B) has been dated at 3.47 billion years old and thus
(C) have been dated to be 3.47 billion years old and
thus are
(D) have been dated as being 3.47 billion years old
and thus
(E) have been dated at 3.47 billion years old and
thus are

OA IS E.