Riddle #613

Question: Tom and Joe want to sit behind each other in class and the teacher arranges them so they are both happy.

How did the teacher do so?

Question: What do you call a sad bird?

Question: What kinds of balls do dragons play soccer with?

Question: What can be broken but never forgotten?

Question: What tastes better than it smells?

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?