Answer:
Anterior end
Explanation:
You have a pretty good shot at guessing this, because the earthworm has very little going on at the posterior end except the anus. And you probably saw this in lab, too.
I've attached a picture of the earthworm anatomy. Worms can't smell in the strictest sense, but they can use their receptors as kind of a combo smell-taste thing, and those are located in the anterior end.
