a person can swim at a vigorous pace for 30 minutes without getting tired. what is an appropriate long-term goal for this person?

to swim at a vigorous pace for one hour by the end of one week
to swim at a vigorous pace for one hour by the end of two months
to swim at a vigorous pace for 20 minutes by the end of two months
to swim at a vigorous pace for 25 minutes by the end of two months