What is the relations hip between engine displacement and overall (combined) CO2 emissions ? (i. e., when one variable is high/low, what is the value of the other one?)

Shafts are machine elements that are used to a) carry axial loads b) direct shear loads c) transmit power d) rotate at constant speed e) none of the above circular and square shafts subjected to the same torque under the same circum behave a) the same way b) almost the same way