题目内容：

情态动词后能加过去完成时 如 would had done 如果只存在 would have done 是不是had受情态动词变为have

优质解答

情态动词后,一般只能用动词原形.如：He can achieve a high mark if he takes the teacher's advice.如果说他过去没有接受老师的建议,且没有取得高分,此时就可以很惋惜地说：If he had take the teacher's advice,he...