adj.可选择的，选修的

History is an optional subject at the college.
历史学是该校的一门选修课。
Eric doesn't like taking compulsory course but optional course.
埃里克不喜欢上必修课，而喜欢上选修课。
I might go to the gym after work, but it's not certain.
我可能下班后去健身房，但不肯定。
The dress code for the party is optional, so you don't have to wear a suit.
聚会的着装要求是可选的，所以你不必穿西装。
Attending the extra classes is optional, but it can greatly improve your understanding.
参加额外的课程是自愿的，但它可以大大提高你的理解力。
You can choose to have breakfast in the hotel, or you can skip it if you prefer.
你可以在酒店吃早餐，或者如果你愿意，可以选择不吃。
The dessert is optional, so feel free to have it or not.
甜点是可选的，所以你可以随意选择吃或不吃。
The survey includes an optional section where you can provide additional feedback.
调查包括一个可选的部分，你可以在那里提供额外的反馈。
The swimming lesson is optional, so only those who want to participate need to sign up.
游泳课是自愿的，所以只有想参加的人需要报名。
The final exam has an optional essay component, which could boost your overall grade.
期末考试有一个可选的论文部分，这可能会提高你的总分。
The software update is optional, but recommended for improved performance.
软件更新是可选的，但为了提高性能，建议进行更新。
The donation to the charity is entirely optional, no one will pressure you.
对慈善机构的捐赠完全自愿，不会有人强迫你。