In the lesson, you say
"Calor" is more commonly feminine in southern Spain and some Latin American countries.This means that in other parts of Spain (i.e. most of it) it is masculine.
The question in the quiz therefore asking if "mucha calor" is correct should therefore accept both answers, yes and no.
Likewise with other nouns which can be both feminine and masculine, what is the point of asking the yes/no question when both are possible? If we look at the "rules" then we have a 50:50 chance of being wrong no matter what we put. So please could you either change the questions, or remove this lesson.