一个很难解释的短文改错题---务必高手进

Many people say, “No pains, no gains.” I think it’s right.
Nothing can be done without working hard.
If you want to do something successfully,
you must try your best, For example,
Madame Curie and her husband has been working for many（has改had）
years. At last, they were successful in finding radium.
Diligence is a important key to success. Nearly all of
the great men worked hard as they were young.
On the contrary if you have nothing to do, you’ll become
lazy. Your mind will not be bright. Even more worse, you
will be in low spirits and idle away your time.
括号里的为改正的。
我就答案是“has改成had”，我就不明白为什么要改成“过去完成时”
请高手指点

句子讲的是居里夫人和她的丈夫努力工作发现了镭元素，这就是过去完成的事情啊，要是用has的话就表示他们过去到现在一直努力工作，跟事实就不符了

你说的没错 however 使用逗号 but 不用逗号 但是 这个句子是特殊的 因为but后面还有一个to their（her）surprise呢 这是插入语句 插入语句 前后必须有逗号 这也是定律 所以没有错 就应该是这样 再说 改错没有改标点符号的 谢谢 希望我的回答能帮助你