List an example of each of the following:

a. Two quantitative variables that are likely to have a positive linear relationship.

b. Two quantitative variables that are likely to have a negative linear relationship.

c. Two quantitative variables that are likely to be independent.

d. Two quantitative variables that are likely to have a curvilinear relationship.

e. Two nominal variables that are likely to be associated.

f. Two nominal variables that are likely to be independent.