通常情况下,由and连接的两个主语从句,意思都是紧密相联的,当做一个整体,谓语动词用单数.如：What caused the fire and what was the loss is unknown. 通常情况下,由and连接的两个主语从句,意思都是紧密相联的,当做一个整体,谓语动词用单数.如：What caused the fire and what was the loss is unknown.