'When one team of researchers interviewed fourth-, fifth- and sixth-graders at an urban California high school, they found that more than half of them didn’t know pickles were cucumbers, or that onions and lettuce were plants'. 

Anyone living in more rural areas would know chocolate milk doesn't comes from brown cows. Rural area are typically Republican voters. On the other hand urban individuals would be more likely to think something along those lines typically Democrat voters.
Common sense and logic!!