A:45°
B:60°
C:120°
D:135°
如图,AB是半圆的直径,点D是弧AC的中点,∠ABC=50°,则∠DAB的度数是____.
以下实验操作错误的是 ( )
一小船在静水中的速度为3m/s,它在一条河宽150m,水流速度为4m/s的河流中渡河,则该小船( )
Our government has tried many ways to the smog(雾霾)problem. Maybe we'll have a clear sky in the near future.