一、动词ing的具体形式
[观察例句]
①They sat in the classroom，reading the books borrowed from the library.
②I stood there motionless，not knowing what to do.
③Having succeeded in the test，he became more confident.
④Not having finished his homework，the boy was still doing it in the classroom.
⑤Having been told several times，he still couldn't understand how to operate the machine.
[归纳用法]
(1)动词ing(以do为例)从形式上可分为一般式(doing)与完成式(having done)，其被动式分别为being done与having been done。
(2)动词ing形式的一般式作状语，表示的动作与谓语动词所表示的动作同时或相继发生，其否定式为not doing。
(3)动词ing形式的完成式作状语，表示的动作发生在谓语动词所表示的动作之前。其否定式为not having been done。
