问题
_____ the students in our class is 45 and _____ them study hard. [ ]
A: The number of; the number of
B: A number of; the number of
C: The number of; a number of
D: A number of; a number of
B: A number of; the number of
C: The number of; a number of
D: A number of; a number of
正确答案是：
