Question

Which is not a school supply?

Answer 1

C. El brazo is the answer.

Answer 2

El brazo

Why? 
A) El libro = The book, we need books in school so this is a school supply.

B) El lápiz = The pencil, we need pencils to write in on things so this is a school supply

D) La hoja de papel = A sheet of paper, we often write notes on paper so this is a school supply.

Finally, C) El brazo is an arm, this is a body part, not a school supply.

This is how we know the correct answer, which is not a school supply, is C) El brazo.

Hope this helps!~