There are different types of air masses that coming from different locations that influence the weather in north america. a: 6; 4 b: 6; 6 c: 2; 4 d: 4; 6edit: nobody answered, but i turned in the quiz got the result. the answer is d, 4: 6

The answer to the question is : B: 6;6
There are __6__ different types of air masses that coming from _6___ different locations that influence the weather in North America., namely :
a) Continental Polar ; Large sub polar land area   b) Continental Arctic ; Canada, United States   c) Continental Antarctic ; Antartica  d) Continental Tropical ; Sahara, Arabian & Australian Deserts  e) Maritime Polar ; Polar Oceans  f)  Maritime Tropical ; Rocky Mountains

So  if  the sum of the enthalpies of the reactants is greater than the products, the  reaction  will be  exothermic.  if  the products side has a larger enthalpy, the  reaction  is  endothermic. you may wonder why  endothermic reactions, which soak up energy or enthalpy from the environment, even happen