Choose the correct option to complete this tense corporate boardroom email.

If the board of directors won't hold the CEO accountable, then the shareholders _____.

The correct answer is must.

This sentence uses Verb Phrase Ellipsis. Instead of repeating the entire phrase "hold the CEO accountable," we can drop it entirely and just use the modal verb "must" to stand in for the whole idea.

"Must hold" is grammatically incorrect here because "hold" is a transitive verb and requires an object immediately after it. "Must do" and "must have" use the wrong auxiliary verbs for this context.