extra来源
extra的来源为：ex（向外）+tra（形容词后缀）
例句
1、In terms of extra staff ─ how many will we need?
就额外的员工来说，我们需要多少人？
2、An extra £ 10 million in foreign aid has been promised.
额外的1000万英镑外国援助款项已得到保证。
3、They won by a single goal after extra time.
他们在加时赛中仅踢进一球即获胜。