Mechanical weathering is also called weathering.

aa

explanation:

literally the answer is aa. not kidding. aa is a group.

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.        

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.

where are the choices