Which of the following is a threat to human health due to global warming?
a. rising sea levels and coastal erosion
b. increased droughts, hurricanes, and floods
c. accelerated extinction rates of plants and animals
d. all of the above are possible threats to human health due to global warming.

I'd say D. All of the above are possible threats to human health due to global warming. 

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