The question is a mess!!!
The question asks for the efficiency of the accounting department vs other.
In that case Option E) is a trap because, they have the best accounting in the COMPANY.
Option C) is irrelevant. Premise states that efficiency comes with experience NOT degree.
and coming to Option A) - Quite interesting - because of the word Significant.
If an employee of many years experience from BookKeepers joins Auditors, then surely the gap between employees experience at Auditors and Bookkeepers will be SIGNIFICANT.
However still MANY is not equal to MOST.
100 employees out of 1000 is still many but not most. Hence Option A - is also wrong.
None of the options weaken.
However Option B) could be the answer if we assume that it wasn't in-experience but their own internal trouble that let down Auditor's Inc.