Why are researchers trying to make new vaccines for more diseases ? a. to control diseases and prevent epidemics b. to encourage different pathogens to mutate c. to prevent a worldwide pandemic d. to make money for pharmaceutical companies

What makes the yardstick test a direct measurement of reaction time? a. the further the yardstick falls, the slower the reaction time. b. yardsticks have numerical markings for length. c. yardsticks are designed to measure reaction time. d. all of the above select the best answer from the choices provided.