Although the researchers agreed unanimously on their

Do you mind explaining why other options are incorrect? Thanks.

I believe Option B is correct :- first it is direct and when is the more appropriate preposition..

from what I remember the answer key said B was idiomatic, "surprised when"

A - is passive voice instead of active voice
C - "in evidence" is wordy/akward
D - "as" is not idiomatic

Basically you need active voice and surprised..when

Although the researchers agreed unanimously on their expectations for the outcome of the experiment, their surprise was evident when the actual data started coming in.

* their surprise was evident when
* they were evidently surprised when
* their surprise was in evidence when
* they were evidently surprised as
* they were surprised as

We have a contrast here, so I prefer parallelity in subjects -
Although the researchers....., they
This rules out A and C, because THEIR is a possesive pronoun. As a thumb rule:
A possessive pronoun can have either a possessive or a non-possessive noun as its antecedent, which is not the case here.

I ruled out E because it omits the adverb evidently, which one should not do unless one has a strong reason. Moreover, as is incorrect here. We dont have any comparison of clauses here. If you noticed, we have surprised, which indicates some post experiment action i.e., implying something related to time. So, both D and E are out.

I googled on surprise as, but found that correct one will be surprise at/when


Plug-in B in the original senetence:
Although the researchers agreed unanimously on their expectations for the outcome of the experiment, they were evidently surprised when the actual data started coming in.
[Sounds correct. when the data started coming in indicates there has to be some time moment]

Although the researchers agreed unanimously on their expectations for the outcome of the experiment, they were evidently surprised as the actual data started coming in.