Final answer:
The remaining juice is represented by the fraction 1/4 (option a).
Step-by-step explanation:
To find the fraction that represents the remaining juice, you need to subtract what was poured from the total. Since the waitress poured 3/4 of a gallon, the remaining juice is 1 - 3/4 = 1/4 of a gallon. So the fraction that represents the remaining juice is 1/4 (option a).