13．A．difficultB．usefulC．easyD．interested
13．
A．difficult
B．useful
C．easy
D．interested
相关考题：
The speaker believes that .A.music is a spoken languageB.music develops as we grow upC.music is above the other artsD.music plays an important part in our life
下列各命题都成立，写出它们的逆命题。这些逆命题成立吗？(1)两直线平行，同位角相等；(2)如果两个实数是正数，那么它们的积是正数；(3)等边三角形是锐角三角形；(4)线段垂直平分线上的点到这条线段两个端点的距离相等。
30． Mr Henry didn’t exchange seats becauseA． there was no man opposite to himB． he had fallen asleep on the train ．C． he hadn’t known he had been able to do soD． somebody sat opposite to him