pair作名词时,其后跟动词的单数还是复数形式取决于所指的是看作一个整体的一件东西,还是两个事物或人的组合:
A good, supportive and protective pair of trainers is essential...(一双兼具支撑性和保护性的好的运动鞋是必不可少的)
The pair are still friends and attend functions together(他们俩依然是朋友,仍一起出席一些社交活动)。
A pair of shoes is black.
Two pairs of shoes are black.