—__________.
A:Good luck.
B:Congratulations.
C:Have a good time!
D:It doesn't matter.
用方框中所给的短语的适当形式填空。
hear from, arrive at, be good at, as well, be afraid of
如图,四边形ABCD是菱形,∠ABC=120°,AD=2,则对角线AC的长是( )