Select the most appropriate word to fill in the blank
The ______ part of this issue is that the investigation officer himself turned out to be the culprit.

Options

A. funniest
B. major
C. real
D. primary

Explanation

Funniest - something or someone that causes laughter.
Major-more important and bigger than others of the same type. Real-Truth, existing in fact not imaginary.
Primary-Most important,Main So, the option (a) is the most logical answer