Sketch a graph to illustrate your idea of each of the following relationships. Be sure to label both axes appropriately. In each case, explain under what circumstances, if any, the curve could shift:

a. The relationship between a person's age and height -

b. Average monthly temperature over the course of a year

c. A person's income and the number of hamburgers consumed per month

d. The amount of fertilizer added to an acre of land and the amount of corn grown on that land in one growing season

e. an automobile's horsepower and its gasoline mileage (in miles per gallon)