elective

Most university students take at least one elective course to broaden their knowledge outside their major.

(Chinese) 大多数大学生至少会选修一门选修课，以拓宽主修专业之外的知识。

The surgeon explained that the knee replacement was an elective procedure, not an emergency surgery.

(Chinese) 外科医生解释说，膝关节置换术是一项可选的手术，而不是急诊手术。

She decided to take photography as her elective this semester instead of music theory.

(Chinese) 她决定这学期选修摄影课，而不是音乐理论课。

High school students often have more freedom to choose their electives during their senior year.

(Chinese) 高中生在毕业年级通常有更多的自由来选择他们的选修课。