optional
adj
that may be chosen or not, as one wishes; not compulsory 可选择的; 随意的; 非强迫的
optional subjects at school 学校的选修课
Formal dress is optional. 是否穿礼服自便.
The cassette player is an optional extra in this make of car, ie It will cost extra if one chooses to have it. 这种型号汽车如需盒式磁带唱机费用另计.
So I called on you and asked if I could borrow some jewellery. Do you remember now?
于是我去看望你,问你可不可以借给我一些首饰。现在想起来了吧。
On our way home that night I looked down and saw that the necklace was not around my neck any more. I told Pierre. We rushed back to the palace and looked for it.We asked everyone there if they had found a necklace, but without luck. We couldn't find it;