Definition: In this task, you will be presented with a multiple-choice question in Persian, and you should answer the question based on your knowledge. Classify the answers based on options.
Input: نسبت سن یک برادر و خواهر که هر دو دانش آموز دبیرستان میباشند، 6 بـه 5 اسـت. حـداقل سـن خـواهر
کدام است؟  <sep> (A) 5 سال (B) 10 سال (C) 15 سال (D) 20 سال
Output:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
C