op·tion·al
adjective/ˈɒpʃənl/
/ˈɑːpʃənl/
- 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，另一些是选修的。 - 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.
这些功能可以作为软件包的可选部分提供。
Oxford Collocations Dictionaryverbs- be
- make something
- entirely
- purely
- Certain courses are compulsory; others are optional.