a boy and girl

a boy and girl This is a boy and a girl.为什么不说these are a boy and a girl. Each boy and girl . girl and boy boy and girl man ,woman ,child ,a boy and a girl的复数 I am a boy and you are a girl a girl and a boy谓语用单数还是复数 many a boy and a girl 单数还是复数 there（）a boy and a girl in the room. many a boy and many a girl __(be) clever every boy and every why boy and girl no easy be a good firend?