Groups of people who vote at higher rates have

Single-subject designs can improve on the pretest-posttest designs by

A) adding a control group. B) adding an additional single-subject as a hypothetical control. C) adding more conditions to the experiment. D) using a better statistical test to evaluate the data.

World population is growing mainly because

a. people are having more children. b. immigration is at such high levels. c. mortality has decreased so dramatically. d. agricultural yields have grown so exponentially over the last decades.