Many have heard me riddle

Question: Many have heard me, but nobody has seen me, and I will not speak back until spoken to.What am I?

Question: What do you call a sad bird?

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

Question: What has a bed that you can't sleep in?

Question: How are doughnuts and golf alike?

Question: What cannot be seen or felt, but can only be broken by voice?