The boss is . . . . . . . . leave still. A. on B. by C. to D. in

The correct answer is C. to.

The boss is to leave still. This means that the boss is still planning to leave, but has not yet done so. The other options are incorrect because they do not make sense in the context of the sentence.

• A. on is incorrect because it suggests that the boss is currently in the process of leaving.
• B. by is incorrect because it suggests that the boss has already left.
• D. in is incorrect because it suggests that the boss is going to leave at some point in the future.

I hope this helps!