Which statement is true about exercise and health

Me with this i need to get the answer quickly.

[120 total points] (public health) in one of the largest human experiments ever conducted, in 1954 a randomized controlled trial was run to see whether a vaccine developed by a doctor named jonas salk was effective in preventing paralytic polio. a total of 401,974 children (ages 6–9), chosen to be representative of those who might be susceptible to the disease, were randomized to two groups: 200,745 children (the control group c) were injected with a harmless saline solution (a placebo) and the other 201,229 children (the treatment group t) were injected with salk’s vaccine. what was the point of giving saline solution to the children who didn’t get the vaccine? explain briefly.

What is difference between an epidemic and a pandemic? a) an epidemic is a disease; a pandemic is a treatment. b) an epidemic is restricted to a local region; a pandemic is global. c) an epidemic has low mortality; a pandemic has higher mortality. d) an epidemic is caused by a bacterial infection; a pandemic is caused by a viral infection.