—I don't know _________ or not Simon will come here.

—Don't worry. ________he comes, I'll call you at once.[ ]

A. whether; Whether  

B. whether; If  

C. if; Whether    

D. if; If

轮船、鸭子能漂在水面上，这是因为它们受到了水的______作用．在水中下沉的物体______（填“受到”或“不受”）这个力．