The maths teacher demanded that all the students _______ the examination paper within one and a half hours.

A．would finish　

B．finished

C．finish　

D．could finish

请从所给的四个选项中，选择最合适的一个填入问号处使之呈现一定的规律性。（）

A.选项A

B.选项B

C.选项C

D.选项D