可选配件；可有可无的东西

任选附件

optionality───可选择性

optional hyphen───可选连字符

National City───国民城市银行；纳欣诺市（美国加利福尼亚州西南部城市）

National Park───（美）国家公园

fractional extraction───分步萃取

national debt───国债

national epic───民族史诗

Too busy getting on with life, many seemed to have jettisoned courtesy as an optional extra.───由于过于忙的要应付生计，许多人似乎投弃了谦恭，把它当成是可选择的额外部分。

A simple idea would be to sell access to the quiet carriage as an optional extra when the ticket is bought.───只需在售票时为安静车厢额外收费，就可轻松实现这一想法。

Why does this have to be an optional extra and not part of the basic package?───为什么有那么多余的可选功能而不是只有最基本的功能 呢 ?

The system includes speakers and an amplifier. A projector security cage is an optional extra.───该系统包括还包括一个扬声器和放大器。

A holiday isn't an optional extra. In this stressful, frantic world it's a must.───休假并非可有可无。在这个紧张而忙碌的世界，它是必不可少的。

The car radio is an optional extra.───汽车上的收音机是可选择的额外配件.

The cassette player is an optional extra in this make of car.───这种型号汽车如需盒式磁带唱机费用另计.

Constructors have optional extra parameters for the comparison object.───构造函数有可选的额外参数用于比较用的函数对象.

Music is an optional extra at our school.

No, sorry, massager is an optional extra.

An optional extra is a rainfall monitor.

Leather seats are an optional extra.

Reading is not an optional extra.

Cruising chutes are available as an optional extra.

Return flight back to U.K. or optional extra day in Stockholm, for sightseeing or a visit to a local woodworking group.

What optional extra security devices are available?

Atheism for Marxism is not an optional extra or a mere facet but the very essence of it.