Where_____(be) the boy and the girl.请问为什么？

are(现在进行时BE动词) / were(are的过去式)

复数所以用are或were

are/were，因为主语是 the boy and the girl，所以谓语就要用复数的 are或者were(过去式).

are

因为the boy and the girl是复数

are 主语是the boy and the girl,是两个人

are/were

are 现在在哪里?
were 以前在哪里?