-many times,the boy still didn't know how to do the exercise

Having been told ,这是非谓语动词,不是现在完成进行时,having 这里用-ing 是非谓语动词的形式之一,加ing表示这个谓语的动作与主语是主动关系,这句话可以写成:the boy has been told many times ,the boy still didn't know how to do the exercises.这样就成了两个独立的句子,因为一个句子不能出现两个谓语动词,要想改成一个句子,要么加连词,要么其中一句改成非谓语动词,就如例句的一样.