Monovalent and bivalent OPVs respectively contain one or two types of attenuated poliovirus, reducing the number of strains that could possibly mutate.

一价和二价口服脊髓灰质炎疫苗分别含有一种或两种毒脊髓灰质炎病毒，少了可能发生突变的毒株数量。

The law of one price means that in the absence of transportation costs and official trade barriers, it is agreed that the price of a commodity in different regions should be the same for the same currency.

一价定律意味着，在没有运输成本和官方贸易壁垒的情况，一致认为，同一种货币在不同地区的商品价格应该相同。