Earthquakes happen when

a : magma fills the chamber in a mountain
b : seismic waves are transferred from the ocean floor to ocean water
c : tectonic plates suddenly move past one another
d : rocks are broken down and transported from one place to another

i think ninja is the best

answerenforce the organization's security policy;

the major difference between the two is the objective and the reward of the game. candy crush has a puzzle theme with the objective of meeting a specific quota of points or objects, you are able to gain access to the next level and compete with peers on the process. on duolingo the objective is rather different, you are given sets of questions for you to answer for you to move to the next level and as for the reward, you are able to learn available language as this is an app developed to teach the user about other languages.