A because the rest doesn’t make sense if you say it with the whole sentence
Rojo, negro, una calavera o una crus
The answer is "Yo"
this is the answer because "Laura" is saying her opinion.
Not "nosotros"(we) because she is talking about herself.
Not "tu"(you) or "ellas"(they fem.)because it doesn't match up with the verb used in the sentence "creer".