1He has a friend who____ the piano very well.这种句型里的单词要加s还是原型?
2 I didn't know________.
A where does he live B where did he live
C where he lives D where he lived
这种句型的问句是怎么判断的?
3 Where_________live before you came here?
A did you used to B did you use to
C ues he to D he used to
这题为什么选B不选A呢?
第一题如果只有第三人称单数要不要加s呢？