He is often heard to___(sing) songs in class. 括号里应怎样填,为...答:而“hear sb.do sth.”则表示“听到整个动作”,或者意为“听到这个动作完成了”.———在feel,hear,listen to,look at,notice,observe,see,watch,have,let,make等词后的补足语中,不定式不带to.但是这些句子如果变成被动结构时,就必须带to.例如:I often hear him sing the song.He is often he...