They hope to stand the top of the mountains one day.
A:at
B:on
C:to
D:in
—I've got a headache.
—No wonder.You in front of the computer too long.
如图,△ABC中,D、E分别为AC、BC边上的点,AB∥DE,CF为AB边上的中线,若AD=5,CD=3,DE=4,则BF的长为( )