By the time the police arrived ,they (kidnap)the poor boy successfully yet.
问题描述：
By the time the police arrived ,they (kidnap)the poor boy successfully yet.
答
had not kidnapped
过去完成时 （指过去的过去）
如不明白请追问
手机提问者如果满意，请在客户端右上角评价点“满意”即可
如果有其他问题请采纳本题后另发点击向我求助，答题不易，请谅解，谢谢。
祝学习进步
答
hadn't kidnapped
由arrived知是过去完成时,又由yet知道要用否定.
整句话意思是,直到警察赶来时,他们还尚未成功劫持那可怜的男孩.