A young girl in a polka dot dress plays on a beach is a synonym of a girl plays at the beach.
This justifies what answer for what question? Q & A:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Given the sentence "A young girl in a polka dot dress plays on a beach." is it true that "A girl plays at the beach."?
yes