若|x|=﹣x,则x是[ ]
A.正数
B.负数
C.负数或零
D.正数或零
答案:C
_______for the captain ,the ship would have sunk with all on board .
A. Hadn’t it been
B.Had it been not
C.Not had it been
D.Had it not been
采用闭合或附和水准线路测量时,高差闭合差的容许值为()。
A、±2√nmm
B、-2√nmm
C、±√2nmm
D、-√2nmm