Find superfluous word

In general, my daughter asked, 2nd class assignment - to guess the word and find the extra word.
4 words - angle cone, square, circle

My solution:
First corner - all the pieces remaining closed, no angle
Second - cone is volumetric figure, the other on the plane

So no !!!
The answer - a circle and a square, so the teacher said. True to explain why - difficult

Or that I do not understand, or education finally died.