Answer:
A. first, highest in rank or importance
Step-by-step explanation:
The word principal can mean a crossbar, a sum of money, the highest authority in an organization and something that comes first in order of importance.
In the example sentence, principal is an adjective which modifies the noun it follows, objective. Thus, the right definition of a word is the one that is more suitable according to the word category and context that surrounds it. Actually, the sentence means that the main purpose or goal of the club is to raise money to get new band uniforms.