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
网友回答
A. settled down
(答案→)B. set out
C. took off
D. turned up
解析：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。