The key difference between an experimental and a quasi-experimental study is that the quasi-experimental study

Explanation:

            An experiment or a true experiment is an experimental study where the experimenter tries to evaluate or estimate whether any treatment or an intervention makes a real difference in the measured outcome. It includes the following elements -- control, random assignment and the manipulation of the independent variables.

          Whereas in quasi-experimental study, random assignment as well as control group are not necessary.

two jet streams that directly affect the formation of weather in the continental part are a polar jet and a subtropical jet. they are responsible for the transportation of weather systems, which directly affect people. the polar front is the boundary between cold air from the north pole and warmer equatorial air. both the polar jet and the subtropical jet blow from the west to the east, and follow the boundary between cold and warm air.

the strongest jet streams are polar jets, while subtropical jets are somewhat weaker.

the right answer is c. the polar jet stream is generaly stronger than the subtropical jet stream.