Answer:
D. "coach" isn't supposed to be capitalized, as it isn't a proper noun (we know that because it says "the" in front. If it was just "coach" and there wasn't a "the", it would be a proper noun and "coach" would have to be capitalized). As it isn't capitalized, we can rule out B and C. "Let's" has to be capitalized because it is dialogue, and is just like the start of another sentence. Thus, the answer is D.