![a pair of (一対の)](https://pooh.aadacoda.com/wp-content/uploads/2018/08/grammar-e1602584346774.jpg)
a pair of
組になっているもの→単数扱い
A pair of sunglasses is what you'll need there.
2つ一組のもの→複数扱い
A pair of dolls were given to me.
a pair of の代名詞は they (複数形)
I bought a pair of pants and I gave then to my brother.
this pair of shoes = these shoes と表現できる
組になっていないもの
a couple of pencils