Answer:
The third answer: Steve will talk your ear off about his favorite varieties of lettuce, so you'd better not mention gardening if you don't want to hear about mulch all night long.
Explanation:
This sentence makes the most sense out of all of them. In the example sentence, it states "so you had better not mention gardening if you do not want to hear about mulch all night long". The first answer says "you've", which is a contraction of "you have", not "you had", so that would be incorrect. The second answer has a misspelled word, and the last one is missing an apostrophe. The third answer is correct.
