Everyone in Biba's neighborhood is permitted to swim at Barton Pool at some time during each day that it is open. No children under the age of 6 are permitted to swim at Barton Pool between noon and 5 P.M. From 5 P.M. until closing, Barton Pool is reserved for adults only.

Question: If all the sentences above are true, then which one of the following must be true?
Options:
A. Few children under the age of 6 live in Biba's neighborhood.
B. If Biba's next-door neighbor has a child under the age of 6, then Barton Pool is open before noon.
C. If most children who swim in Barton Pool swim in the afternoon, then the pool is generally less crowded after 5 P.M.
D. On days when Barton Pool is open, at least some children swim there in the afternoon.
E. Any child swimming in Barton Pool before 5 P.M. must be breaking Barton Pool rules.
Answer: "B"