that you can choose to do or have if you want to 可选择的；选修的 Certain courses are compulsory; others are optional. 有些课程是必修的，其他是选修的。 🔊🔊 This model comes with a number of optional extras (= things you can choose to have but which you will have to pay extra for). 这一型号有一系列可供选择的附件，价格另计。 🔊🔊 These features can be offered as an optional part of the package. 这些功能可以作为包装的可选部分提供。
Oxford Collocations Dictionaryverbs- be
- make something
- entirely
- purely