根据短文内容，选择正确答案。

    Mike had a nice blue cup which he liked best. It was a present from his aunt for his fifteenth birthday last year. He cleaned it once a day and took good care of it. His cat, Mimi, was very naughty(淘气的) and sometimes it could make some trouble(麻烦) for Mike.

    The day before yesterday, the cup was broken(打破) by his cat. He felt unhappy. Susan saw him and asked, "You look sad. What's the matter with you?"

    Mike said, "There is something wrong with my cup."

    Susan said, "Don't worry. I can repair it."

    Mike felt surprised and asked, "Repair? You can repair it? You?"

    "Yes. Believe me! Where is it?" Susan answered.

     "Here. My cup is broken. Are you sure you can repair it?" Mike took out his broken cup.

     "Ha……, I made a mistake(错误). I think your__1__ is broken," Susan said.

    Hearing what Susan said, Mike couldn't help laughing.

一节数学课共 $\frac{2}{3}$ 小时，同学们动手操作用了一节课时间的 $\frac{1}{5}$ ，老师引导讲解用了 $\frac{3}{10}$ 小时，其余时间做作业。做作业用了多少小时?

***诗词《沁园春•雪》中有“江山如此多娇，引无数英雄竞折腰。惜秦皇汉武，略输文采；唐宗宋祖，稍逊风骚；一代天骄，成吉思汗，只识弯弓射大雕，……”根据相关知识回答下列问题：