当and或both…and…连接两个不可数名词或可数名词作主语时,谓语动词用复数形式.但如果并列的两个名词指的是同一个人,同一个事物或一套事物时（第二个名词前往往没有冠词）,谓语动词要用单数.
例1.Plastic and glass are both useful in industry.
A cart and a horse were seen in the distance.
例2.A cart and horse was seen in the distance.