感官动词有see,watch,observe,look at, hear, listen to ,notice有被动语态!
用法：感官动词+宾语+do,在用作被动语态要补出to.
例如:I heard her sing an English song just now.
She was heard to sing an English song just now.see sb do 表示看见某人做的全过程(我们习惯性省掉to do 当中的to) see sb doing 表示看见某人正在做的动作 当某人被看到在做某事的时候,要用 sb be seen to do ,也就是说to就还原所以，在被动语态里用to