I’m glad to you. I know that you’ll come to see me from your letter and I feel very happy.
A:write to
B:hear from
C:hear of
D: look for
下列关于空气成分的说法错误的是( )
如图,△ABC中,DE∥BC,交边AB、AC于D、E,若AE:EC=1:2,AD=3,则BD=____ .