Answer:
to swim at a vigorous pace for one hour by the end of two months
Step-by-step explanation:
'C' and 'D' cant possibly be right cause the goal is to swim for longer not shorter. 'A' can't be right cause you cant possibly learn to swim faster from 30 minutes to an hour in only a week, that just sounds impossible.
im totally guessing here, but i think 'B' is right.