我需要换一些外币。
wǒ xūyào huàn yīxiē wàibì 。
I need to exchange some foreign currency.
在国外旅行时，我们需要使用外币。
zài guówài lǚxíng shí ， wǒmen xūyào shǐyòng wàibì 。
When traveling abroad, we need to use foreign currency.
很多国家的外币汇率都在变化。
hěnduō guójiā de wàibì huìlǜ dūzài biànhuà 。
The exchange rates of foreign currencies from many countries are constantly changing.