Ahh k12 sucks :/ been there but your answer is A !
Weather front is the boundary between two masses of air with different densities, temperature and humidity.There are four types of weather fronts: cold front (cold air mass, thunderstorms and rain) , warm front (warm air mass,smaller density than the cold front), occluded front (low pressure ares), it is formed when cold front overtakes a warm front) and stationary front , the boundary between two air masses that are not strong to be either both cold or both warm (clouds, precipitation).
The answer would be C.fertility rate
Hope this helps
Have a great day/night
Relic Boundary is the correct answer :)