Do you think everyone enjoys their weekends?

这个句子可以还原成Do you think （that ）everyone enjoys their weekends?
这里that 被省略了,它是一个宾语从句.在宾语从句中引导词that 可以省略.如果用to enjoy的话,从句的谓语就变成了 to enjoy ,而to enjoy 是不定式,它不可以做谓语.所以不能用 to enjoy.