Which factor best explains the reason the average summer temperatures are higher than winter temperatures in Northern America?

What do you need with it’s not a question your just stating what it says

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).