Fun Riddles

Question: Surrounded by green, surrounding white.
Inside is red, holding many black babies.

What is it?

Question: 2 men catch 2 fish in 2 minutes. At this rate, how many men could catch 500 fish in 500 minutes?

Question: Travel a mile and I will change.
Travel a million and I will end as I started.

What am I?

Question: Why don't mountains catch colds?

Question: I can be used to build castles,
but I crumble in your hands.
I can help a man see,
and am found all around the lands.

What am I?