尺寸的加工精度是靠夹具来保证的。( )
参考答案：错
— Nancy, what classes are you taking this term?
— _____ I want to take two English courses, or maybe Spanish. [ ]
A. What's up?
B. It's none of your business.
C. I've no idea.
D. I'm not sure yet.
常作防腐剂的是（）
A.山梨醇
B.液体石蜡
C.PEG-400
D.鲸蜡醇
E.羟苯酯类
