A different way to work through this is to read the four parts as one continuous sentence first, checking only for flow and logic, then go back and scrutinize capitalization and word choice separately.
This two-pass method, first for flow, then for capitalization, isolates part (b) as the error, confirming option B.
Let's summarize:
This approach is especially useful when the grammar of every part looks equally clean, because it forces a second, different lens over the same text.
Identify the part of the sentence that contains an error:
"Neither the manager nor the employees ___ willing to accept the new policy."