— How was your trip in Chengdu?

— Not so good. I stayed there for two days. But it rained on _____ of the days.

                                                                                                                                                        [ ]

A. none          

B. neither      

C. both        

D. all

体育锻炼应遵循（）的原则。

A.因材施教

B.周期性

C.提高身体素质

D.全面发展