Answer:
Der Kuli schreibt auf das Papier.
Explanation:
Becuase der Stuhl means in English the chair and and the sentence the pen writes on the chair makes no sense.
The same with der Professor, in E it would be the pen writes on the professor also incorrect.
The last one with die Uhr means the pen writes on the clock which is very weird, so also no.
So the last possibility is das papier which means in E the pen wirtes on the paper that makes sense.
