长途光缆线路施工中,光缆接头盒运到工地分屯点后,对其电气、密封性能随机抽样()进行检查。
A.2%-3%
B.3%-4%
C.4%-5%
D.5%-6%
参考答案:A
Suddenly they noticed a house with two big trees _______ in front of it.
A.to stand
B.standing
C.standed
D.stands
系统真空无法建立,如何判断其原因?