写出6个分子是6的最简分数.
以下几个分数都是分子是a的最简分数:
a7、a手手、ae、a手3、a手7、a手9…
— Liu Fang, I didn't know you can play the Pipa and Guzheng so well.
— Well, actually I ________ it since I was six years old. [ ]
A. plays
B. have been playing
C. played
D. had been playing
现场质量管理的重点应放在()上。
A.提高操作技能
B.检验把关
C.过程因素的分析和控制