—Can you give me some advice on what I said just now?

—Sorry, my mind ________.[ ]

A. has wondered  

B. had wondered

C. is wondering  

D. was wondering

因外加载荷超过了钢材的强度而产生的裂纹是（）裂纹。

A、热疲劳

B、应力腐蚀

C、疲劳

D、过载