分析并找出故障点的正常原则是（）

A.先软后硬，先外后内

B.先硬后软，先外后内

C.先硬后软，先内后外

D.先软后硬，先内后外

No adults would like to admit that they are weaker than children to solve sticky and puzzling problems.()

A. to solve about

B. solve

C. in solving about

D. in solving