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.