φ25H6中的阿拉伯数字“6”，代表该尺寸的（）等级为6级。
参考答案：标准公差
— you please go to the movies with me?
—Sorry, I can't. I do my homework. [ ]
A. Can; have to
B. Could; have to
C. Can; had to
D. Could; has to
哪项不适合开胸心脏按压（）。
A.胸部创伤引起心搏骤停
B.胸廓畸形
C.严重肺气肿
D.心包填塞
E.经常规胸外心脏按压，５分钟无效者
