两个不可数名词做主语,谓语动词用单数 还是复数?

and 连接两个名词做主语时,谓语原则上用复数,但是两个名词若构成一个整体事物时,谓语则用单数.
eg.：The teacher and his son are picking apples now.(老师和他的儿子在摘苹果)
Fish and chips is very famous food.(鱼和薯条是一种出名的食品)