They are eating sandwiches不就行了吗,为什么还要They are eating their sandwicher呢
问题描述：
They are eating sandwiches不就行了吗,为什么还要They are eating their sandwicher呢
答
their 他们的~（物主代词）
They are eating sandwiches.他们在吃三明治（没说明是谁的三明治）
They are eating their sandwiches 他们在吃他们的三明治（说明了是他们自己的三明治）