题目

英语高手进,关于现在完成时的几个问题.
1I have lost the pen which I bought the day before.为什么不能说成
I lost the pen which I have bought the day before.
2 By next sunday she will have stayed with us for three weeks.这句中的will have stayed 怎么解释和运用,为什么不能说成will stayed.
3 I felt much better after I had took the medicine.这句中的had
took 为什么不能用一般过去时took
4 He'll go out when he has done with this book.这句中为什么用现在完成时,而不用一般现在时代替将来时.
若能答疑 感激不尽.谢过.
纠正一下2中最后一句应该是will stay
sorry
.........

提问时间：2021-03-12

答案

1.现在完成时主要表示与现在有关的事 I have lost the pen (所以我现在别的笔写了或者我现在没笔可写了）如果说I lost the pen主要是讲某一时刻的事,主要用于叙述.比如I lost the pen yesterday.（我昨天把笔给丢了）
2.will 后直接加动词原形,will stayed 显然是错误的.will 表示将会发生的事,比如说:She will do it by herself.（她会自己做的）如果表示到某个时间会做完某件事 will后面就加完成时 正如你例句中的 By next sunday she will have stayed with us for three weeks.到下个星期天为止她会和我们算起来已经一起待了3个星期
3.句子错误 应该是I felt much better after I had taken the medicine.一样的道理,表示吃下药后好多了.I felt much better after I took the medicine也是正确的.
4.一般现在时表示一个经常做的事比如I go to school every day.所以这句话要用一般现在时的话应该：He goes out when he does with this book.这样他完成这本书然后出门就是他的一种习惯,是对他一种日常生活的描写.而He'll go out when he has done with this book是指等他完成这本书他将会出门,表示的是将来发生的事