宾语从句,陈述句:YOU are sure that ...be sure ...这是谓语,后面加宾语,宾语是句子所以宾语从句的引导词
表语从句是直接放在be动词之后做表语,构成主系表结构
宾语从句是放在及物动词之后做宾语,构成主谓宾