optional

完全可选

To emphasize that something is completely a matter of choice, with no obligation.

强调某事完全是个人选择，没有任何义务。

纯粹可选

To emphasize that the only characteristic of something is that it's a choice.

强调某事的唯一特性就是它是一个选项。

是可选的

Used to state that something is not required or mandatory.

用于说明某事物不是必需的或强制性的。

使...成为可选

Used to describe the action of changing something from being mandatory to not required.

用于描述将某事物从强制性更改为非必需的操作。