圆括号

例句：

1. 1. The equation has two unknowns: x and y.
   这个方程有两个未知数：x和y。
2. 2. He wrote the answer in round brackets.
   他在括号里写了答案。
3. 3. The book is divided into chapters with round brackets.
   这本书用圆括号标记章节。