Riddle #371

Question: You have found a mutant algae that doubles in size every hour. It takes 18 hours for one algae plant to take up half of a certain lake.

How long would it take for two of these plants to take up half of the same lake?

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

Question: What can be broken but never forgotten?

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?

Question: What tastes better than it smells?

Question: What loses its head in the morning and gets it back at night?