Best riddles with simple answers

What do the dentists call the astronauts cavity?

I get whiter the dirtier I get. What am I?

What is a frog’s favorite year?

What has a foot but no legs?

Which is the rope you never skip with?

What is red but it smells like a blue paint?

If you have me, you want to share me. If you share me, you haven't got me. What am I?

I drift forever with the current down these long canals they've made. Tame, yet wild, I run elusive, multitasking to your aid. Before I came, the world was darker. Colder, sometimes, rougher, true. But though I might make living easy, I'm good at killing people too.

Die without me, Never thank me. Walk right through me, Never feel me. Always watching, Never speaking. Always lurking, Never seen.

Only one color, but not one size. Stuck at the bottom, yet I easily fly. Present in sun, but not in rain. Doing no harm, and feeling no pain. What Am I?