$7.$ In figure A$1\mathrm{.}8,$ an increase in z leads to a: a$)$ movement up along one of the lines showing the relationship between x and y b$)$ movement down along one of the lines showing the relationship between x and y c$)$ rightward shift of the line showing the relationship between x and y d$)$ leftward shift of the line showing the relationship between x and y e$)$ trend change in both x and y $8.$ In Figure A$1.8,$ ceteris paribus, an increase in x is asseciated with a: