A boulder is a really, really big rock.
You can't pick up a boulder, but you can sit on it.
The sport of bouldering came from climbing on boulders.
A cement block is heavier than a brick.
A mountain is definitely much bigger than a hill.
A mountain is definitely way bigger than a hill.
If you wanted to climb a mountain, you would need special equipment.
A lake is a large body of fresh water.
A lake doesn't have salt in it.
A pond is a very small body of fresh water.