What Am I Riddles

Question: I climb to the top I dive below I return again For another show.

Question: I go into the water red and come out black.

What am I?

Question: I am a nice word composed of five letters, but the Romans would call me a numbers.

What am I?

Question: If you're looking for something sweet I know what to do.
But if you don't like heat I'm not for you.

What am I?

Question: What has classes but moves?