1.while后面直接加动词时,动词形式一般要分为两种情况.
2.如果该动词和主句主语之间为主动关系,则一般用其现在分词形式即Ving.
如：While watching TV,I heard a knock at my door.
= While (I was) watching TV,I heard a knock at my door.
3.但是,如果该动词和主句主语之间为被动关系时,则用其过去分词形式.
如：While beaten by his father,the boy cried.
= While (the boy was) beaten by his father,the boy cried.