Compra un cuaderno en
a. la tienda de ropa
b. una hoja de papel
c. los materiales escolares
d. la papelería

The correct answer is D: la papelería.

Explanation:

The correct answer is D because la papelería is the stationery shop (the place where we buy writing materials), e.g. a notebook (un cuaderno).  

Tienda de ropa means the clothing store, so we would use it to buy some clothes, not a notebook;

e.g.  Compra una falda en la tienda de ropa.

Una hoja de papel means a sheet of paper, so it can not be considered as the correct answer, while los materiales escolares refers to the school supplies which is not the place where we can buy  a notebook.

answer; (73%);