Answer:
A). First, highest in rank or importance.
Step-by-step explanation:
As per the question, the definition that best assists the readers to find the correct meaning of the word 'principal' in the given sentence would be 'first, highest in rank or importance' as it only goes with the context or meaning of the sentence. Therefore, the sentence would imply that 'the first(principal or primary) objective of our booster club is to raise money for new marching uniforms.' The other options do not correspond to the context of the question. Thus, option A is the correct answer.