— I'm sorry I stepped on your shoe; it was an accident.

— It wasn't! You did it ____. [ ]

A. on purpose

B. by chance

C. by mistake

D. by accident

钢材经历了应变硬化（应变强化）之后_____。

A.强度提高

B.塑性提高

C.冷弯性能提高

D.可焊性提高