Determine whether each of the following situations describes a positive association, a negative association, or no association.

a)adolescents who spend more time on sedentary activities tend to have larger waistlines than those who spend less time on sedentary activities.

b)in patients undergoing hemodialysis, leptin levels are unrelated to the length of time the patients have undergone dialysis.

c)a 1 degree c increase in average temperature between february and april leads apple and cherry trees in germany to blossom nearly five days earlier.

d)among different genotypes of wheat, shorter plant heights are associated with lower grain yields.