Which error in the sentence should be corrected while editing?

We needed to have a security report otherwise, we wouldn't go.

A. awkward sentence

B. wordiness

C. punctuation

D. spelling error

The correct answer is (C). There are two possible sentence as the Conjunctive adverbs join two independent clauses:

We needed to have a security report; otherwise, we wouldn't go.

Or

We needed to have a security report. Otherwise, we wouldn't go.