压力容器的安全状况可分为（）个等级。
A.2
B.3
C.1
D.5
参考答案：D
Your application form must be ________the company you are applying to before Friday.[ ]
A. donated to
B. sent in
C. submitted to
D. handed in
机械产品零件的典型失效模式可以划分为（）区域。
A.早期失效
B.正常工作
C.功能失效
D.晚期失效
