每天十个英语四级高频词汇(11)

optional word 任选字; 随意选择字

optional stipulation 选择性规定   

optional sampling 任意抽样

It is optional with you.

悉听尊便。

If it is difficult to state definitely one or several ports, optional ports can be adopted.

假如难以明确写出一个或几个港口，就可以采用选择港这个办法。