船舶沟通与通信的障碍主要是：（）
①物理障碍②人为障碍③语言障碍④地理障碍
A.①②③④
B.①②③
C.①②
D.①②④
参考答案：B
(2013·高考陕西卷)The children________lost in the woods；otherwise，they would have been at the lakeside camp as scheduled.
A．must have got
B．must get
C．should have got
D．should get
挖填方交界处，填土低于（）的路堤都不应在冬期填筑。
A．1m
B．2m
C．3m
D．5m
