Logic Riddles

Question: What always goes left but constantly goes down.

Question: How can twins be born in different years?

Question: If there were ten fish in an enclosed tank, and four swam away, three died, and three drowned, how many fish would be left?

Question: Surrounded by life , yet life is its biggest enemy. But without life there is no need for it to exist. What is it?

Question: The more you add, the less it weighs.