Answer:
c) keith knew that it was his sister's birthday, and he didn't want to make a big deal about it.
Step-by-step explanation:
We don´t know what does keith do not want to do a big deal about, it could be that it happened something bad to him at school, or that he is down because he broke up with his girlfriend, the sentence that better expresses with no negative or positive connotation, like saying that he didn´t want to make a big deal out of his sister´s birthday, is the third one, "keith knew that it was his sister's birthday, and he didn't want to make a big deal about it"