we spend a lot of time practicing our oral English after class是demand的宾语从句
demand 用法：
demand to do; demand that…,demand of sb.to do sth.
demand 用法：
demand to do; demand that…,demand of sb.to do sth.
Note:后面的宾语从句要用虚拟语气.即：demand that sb.(should) do的形式.