The students expect there to be more varieties of food avail

there是和后面系动词组成there be句型.这里用了expect (sb.) to do (sth.)的句型.可以认为there to be是用在to do句型中的固定用法.这句话也可以改成宾语从句The students expect that there are more varieties of food available in the canteen.学生们期待在这个自助餐厅里可以有更多的食物选择.