My uncle works in a factory that____toy cars(produce)

题目

My uncle works in a factory that____toy cars(produce)
最好能解释下为什么

答案

My uncle works in a factory that____toy cars(produce)
用produces,第三人称单数.
factory是单数第三人称的主语,故produce 要加S 变为单三,如果主语是复数 那谓语动词要用复数的produce