Need help on daughter's homework

I'm trying to help my daughter on hidden meanings with pictures. It's too tough for me.

What is this?
0
---------
B.S.
M.A.
Ph.D.

The letter on the top of the line is zero. It doesn't look like an letter 'O' to me.

Example 1

man
---------
board

this is "man overboard", I think

Example 2

head
----------
heels

this is "head over heels"

Three degrees below zero.