I am _in_ the classroom.
I am not _at_ the blackboard.
I am _at_ the desk.
There is a book _on_ my desk.
My pens and pencils are _ in_ my pencil-box.
The pencil-box is _in_ my bag.
The bag is _ under_ the desk.
We’ve got flowers _in_ our school park.
Two pupils are sitting _under_ the tree _in_ this park now.