Bill with his mother often 后面加do,还是does?

问题描述:

Bill with his mother often 后面加do,还是does?

does
主语是Bill,with his mother表示一种伴随状态,即mother不在主语之列

does.
with his mother 介词短语作插入语成分,不影响主语的单数形式。
如果是and就要用do。

当然是 does 主语是 Bill
次句改成 Bill often does...with his mother 就显而易见了

dose