Stimulants
a. can slow down the brain's reactions.
b. are not addicting.
c. can excite the central nervous system.
d. can cause ulcers.

Which statement best describes common communicable diseases? a. most communicable diseases are either bacterial or viral and infect the respiratory tract. b. all communicable diseases are viruses that cause pneumonia. c. most communicable disease are bacteria and viruses that infect the intestinal tract. d. all communicable diseases are bacteria that grow in the respiratory tract. select the best answer from the choices provided. a b c d