—Why don't you buy the bike, Mary? — It's too expensive. I can't it.
A:sell
B:lend
C:keep
D:afford
根据如图小芸同学从就读的某中学回到距离40千米远的家乡度假,最便宜的交通方式是( )
如图空间四边形ABCD,E、F、G、H分别为AB、AD、CB、CD的中点且AC=BD,AC⊥BD,试判断四边形EFGH的形状,并证明.