A But I tend to use P Q R for sentences and A for A, now that I have explained it, that should be smaller case.

但是我喜欢用P，Q，R来代表句子，A就代表，我已经解释了，应该是小写的。

youdao

Q comes between P and R in the English alphabet.

英语字母表中，Q在P和R之间。

《牛津词典》

And for that to possibly happen, well, we need certainly some relations between p, Q and r.

要使得这个成立，当然需要一些p, Q, R之间的关系。

youdao