Choose the correct answer

18. It is not hot............ the winter.

A. on         

B. in            

C. at           

D. under

19. I don't like Maths...............it is difficult.

A. and         

B. but         

C. so           

D. because

20. What's the matter............you?

A. in           

B. with           

C. on            

D. of