Sentence Correction

Climate experts, after reviewing this year's recordings of the atmosphere, is not surprised by how warm it has been.

Climate experts, after reviewing this year's recordings of the atmosphere, is not surprised by how warm it has been
MASTER GMAT:
This answer choice is grammatically incorrect. The plural subject Climate experts does not agree with the singular verb is.What helps us identify this question as a Subject Verb Agreement question and identify the mistake is the following Stop Sign:A long complex subject / a long distance between the subject and the verb
After reviewing this year's atmospheric recordings, climate experts are not surprised by how warm it has been
Climate experts are not surprised by how warm it has been after reviewing this year's recordings of the atmosphere
After reviewing this year's atmospheric recordings, climate experts are not surprised by how warm they have been
Climate experts, after reviewing this year's atmospheric recordings, are not surprised by how warm this has been
b
please explain what is wrong withc