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.
Q: Problem: 30 liters of a mixture contains milk and water in the ratio 2: 1. if 5 liters of this mixture be replaced by 5 liters of milk, the ratio of milk to water in the new mixture would be ?
Options: a. 3: 2, b. 3: 1, c. 4: 1, d. 5: 2, e. 2: 1
A:
d