Question

Forty-five students _________ a class is the proper number according to a study in the U．S．, published in a magazine last month．

1. A.
   makes up of
2. B.
   making up of
3. C.
   made of
4. D.
   making up

Answer 1

B
making up of“组成”，现在分词作定语，相当于定语从句who make up of a class。