IMO E

MY two cents:

A is incorrect bcoz has is incorrect here
two actions are not mentioned here
has cited.........had contributed

B
passive
also
that estimated that is looking weird


C
workers hve not cited all this
modifier gap

D
had contribted


E
has estimted .. contribute correct
modifier also correctly used

PS: I think we can solve this by tense only

This question looks very much similar to the following one:

https://www.beatthegmat.com/study-of-us- ... 15655.html

IMO (E) as reason stated by stop@800.

Also, (C) is not a valid choice because it is incomplete construction. We need an auxiliary verb at the end phrase to complete the sentence.

stop@800 wrote:IMO E

MY two cents:

A is incorrect bcoz has is incorrect here
two actions are not mentioned here
has cited.........had contributed

B
passive
also
that estimated that is looking weird


C
workers hve not cited all this
modifier gap

D
had contribted


E
has estimted .. contribute correct
modifier also correctly used

PS: I think we can solve this by tense only

Although E looks best, is the use of present perfect has estimated correct ?

is the study still estimating?

I will go with "e" as well.
use of perfect tense make sense hear, as estimate was done before and still hold true.

OA E