问题如下：
Which of the following statements of exchange rate is least correct?
选项：
A. An exchange rate refers to the price of one currency in terms of another.
B. An exchange rate can hold with only one individual currency.
C. An exchange rate generally related to two currencies.
解释：
B is correct.
An exchange rate refers to the price of one currency in terms of another, and there’re always two currencies involves in an exchange rate.
考点： exchange rate
解析： exchange rate通常表示为一单位的货币可以兑换多少单位的另一种货币，这要涉及2种货币。所以B选项入选，AC选项不入选。
这道题的题干和答案不是特别能明白，可以用中文解释一下吗？
