问题
选择题
They must have gotten to the top of the mountain by now. They_____ before the sun rose.
A．settled down
B．set out
C．took off
D．turned up
答案
B
题目分析：A. settled down定居下来，安静下来，B. set out出发，动身，C. took off脱下，起飞，D. turned up[出现，露面，句意：现在他们一定到了山顶，他们在太阳升起前出发的。所以选B。