The correct answer is - C. Many of these nations have advanced industrial economies.
Many of the countries that are lying on and around the Equator are low developed countries, and they do not have advanced industrial economies. Even if they did had, it was not going to be a reason for the big amounts of diseases in this parts of the world whatsoever, because in those types of economies people are much more protected and secure from diseases because they are working indoors in much better controlled circumstances, and also the medicine is much more advanced and available for the ordinary people.