任选的英文：
option

There are no constraints on your choice of subject for the essay, ie You can choose whatever subject you like
文章内容不拘, 你可任选

logarithms are defined with respect to an arbitrarily chosen constant
对数是相对于一个任选的常数来确定的。

When opening a time deposit account, you may have one of the following renewal options
开立外汇定期存款帐户时，您可以任选以下一种展期方式

optional subjects
选修科目

No highway option.
没什么捷径可言。

Is French compulsory or optional?
法语是必修课还是选修课？

Who has got an option on the building?
谁获得这幢建筑物的买卖选择权？

You have an option on a piece of land.
你有买卖一地皮的选择权。