Over the last decade, my experiences            there is no shortcut to excellence and you have to use your talents and abilities to get ahead of others.

A．had proved

B．prove

C．have proved

D．were proving

显微镜下观察蔬菜叶徒手切片的临时装片，转动细准焦螺旋时，视野中部分细胞图象清楚，另一部分细胞则比较模糊，最可能的原因是（　　）

A．物镜接触玻片

B．切片厚薄不均

C．细准焦螺旋未调好

D．视野太暗，导致物像模糊