测定不透明液体的视密度时，应先将眼睛放在（）的位置上。
A、任意
B、平行于液面
C、稍高于液面
D、稍低于液面
参考答案：C
单句改错。
( )1. This is his the best book. ________
A B C D
( )2. He is taller than any boy in his class. ________
( )3. Which do you like best, this one or that one? ________
( )4. Mike is very cleverer than Jack .________
( ) 5. Kate draws best of her class. ________
货车厂、段修时，限压阀质量保证期限为（）。
A.6个月
B.1年
C.1个辅修期
D.1个段修期
