that's what it is there for.原句是 Why don’t you get some help from the graduate assistance.That’s what it is there for.
问题描述：
that's what it is there for.
原句是 Why don’t you get some help from the graduate assistance.That’s what it is there for.
答
那是他们在那里的原因。
为什么不向那些graduate assistance 求助，那是他们在那里的原因。
there副词前介词省略。
答
这就是它的存在。
答
那就是它存在的原因.
它就是为那存在的.
for what =why
所以原句可改为 That is why it is there.
这样你就理解了