Answer:
D. Elementary schools in Tooten County continue to promote the values of exercise to its students.
Step-by-step explanation:
Even though Tooten County have a lower percentage of young families than a typical country, the retail sales of children's bicycles are above the national average most probably because the elementary schools promote the importance of exercise to its students.
Cycling is one form of engaging in exercise and because it is encouraged, the children tend to make demands for bicycles from their parents.
Other options are simply not viable as a plausible explanation because marketing does not always translate to sales, one local manufacturer's sales would be a small sample size to measure the whole county, where the bicycles are imported from are immaterial, etc.
The most viable explanation would be the the promotion of exercise by elementary schools in Tooten County.