You will be given a definition of a task first, then some input of the task.
Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

Problem: the ratio between the presents of the a and b is 2: 3. if b is 5 years older than a, what will be the ratio of the ages of a and b after 5 years ?
Options: a. 3: 4, b. 1: 2, c. 2: 3, d. 5: 6, e. 1: 3
Output:
a