— Has Tom finished his homework?
— Sorry, I don't know. He ________ it this morning when I saw him.
A:did
B:does
C:has done
D:was doing
右图是一容量为100的样本的重量的频率分布直方图,样本重量均在5,20内,其分组为5,10),10,15),15,20),则样本重量落在15,20内的频数为( )
如图,△ABC中,D,E两点分别在AB,AC边上,且DE∥BC,如果ADAB=23,AC=6,那么AE的长为( )