精基准是用已加工过的高精度表面作定位基准。
参考答案:错
---I’m sorry for losing your book. I will buy a new one for you.
---________. I have another copy.
A.Thank you
B.Happy to hear that
C.Never mind
D.Of course
一辆卡车从静止开始由山顶向山下下滑,卡车司机关闭了发动机,滑到山底速度是 4km/h,如果卡车关闭发动机以初速度3km/h由山顶滑下,则卡车滑到山底的速度是( )
A.
B.
C.
D.