Well lets look at all the choices.
A) This answer isn’t truly safe. If she swims alone and gets hurt there will be no one there to help her. Also, it is good to have someone there for motivation.
B) This seems like a reasonable answer because she warms up before and ends on a slow pace which really prepares her body in an easy but strong way.
C) This is not a safe choice. You should never push yourself too hard on the first try.
D) This is definitely not the thing to do. You never want to eat a large meal right before a workout as this can cause severe cramps.
So, looking at all the answer choices, the best one would be B.