If given these Dif EQ's, I don't quite understand the differences when looking at the direction fields..

a.) dy/dt = f(t,y)

b.) dy/dt = f(y)

c.) dy/dt = f(t)

So for a, the direction field depends on both t and y.. for b, it depends only on the y value, and in c it depends only on the t value..but (if possible) would it be able to show an illustration. I can't picture it.