Riddle me this

Well Just something short and simple for now.

Riddle of the Sphinx:

What walks on 4 legs in the morning, 2 legs in the afternoon, and 3 in the evening?

Another simple one:

There is a patient with a brain tumor. The tumor is inoperable except with a laser. There are four 10Mw lasers that won’t damage the brain, but won’t destroy the tumor. There is one 30Mw laser that will destroy the tumor, but will destroy brain matter as well. How do you destroy the tumor without losing the brain?

And the last one:

A man on one side of a river needs to get a sack of corn, a chicken and a dog to the other side. There is a raft he can use to cross the river, but it can only hold 1 other item besides himself. The man must get each item to the other side. How does he do this?

I won’t post the answers but will send them individually, this way its fair for everyone.

Enjoy the holiday :)