mike with his friends ---- playing chess in the classroom wh

mike with his friends ____ playing chess in the classroom when mr li came in .
这题考with 的用法．请就这个知识点进行说明,be 动词应该跟哪个主语保持一致．
Ais BwasCareD were
在BD之间，不能确定．不知道是应该跟动词前的主语保持一致，还是跟with前的mike保持一致