To me you are right, and the alternative would be the letter a. (although)
Despite would be used with the following structures:
despite + noun
despite + verb + -ing
So, it´s out of question.
Couldn´t be used in one of the following meanings (from 1 to 7).http://michaelis.uol.com.br/escolar/ing ... alavra=yet
And not as a conjunction as well. (see the notes)
It doesn´t fit in the above clause as well.http://michaelis.uol.com.br/escolar/ing ... 22934.html
So, what is left is although
, wich is used with the structures:
although + a clause
Yesss!http://speakspeak.com/resources/english ... ven-though
Be aware that questions like this may be answered with a delay, so in case you need it to homework it´s not good for you.
People around here don´t help cheating, we know that it´s not the case right now, of course.
Congrats on your interest in English matters.