下列对SOP修订描述不正确的是()
A.SOP一经批准不得修改
B.每套SOP最好每年一次更新
C.SOP的任何改变必须由医学主任批准
D.SOP的调整要符合国家政策
参考答案:A
As the saying goes, practice makes perfect, ______is only by using English as often as possible can you learn English well.
A.which
B.as
C.that
D.this
螺纹传动按螺纹幅性质可分为哪几种?设计滑动螺旋的准则是什么?