满足条件M∪{1}={1，2，3}的集合M的个数是 [ ]
A．1
B．2
C．3
D．4
答案：B
They are broading the bridge to _____the flow of traffic.
A．put off
B．speed up
C．turn on
D．work out
失去控制的船舶如何显示号灯与号型
