Can you make the tea Sam

Can you make the tea Sam
Can you make the tea,Sam?
yes,of course I can,penny
Is there any water in this kettle?
Yes,there is.
where's the tea?
It's over there,behind the teapot
原文是这样的,这里behind the teapot
为什么要用the呢.前文中并没有提到过teapot呀
是不是应该用behind this teapot啊
然后后面又问where's the cups?
cups也没有提到过为什么也用定冠词the呢
是不是the可以用在眼睛已经看到的东西呢？