Healthcare costs will rise in the future because . A.
a large group of people will become senior citizens
B.
healthcare providers will charge more for certain types of patients
C.
all medicine will become generic and easily accessible
D.
doctors will refuse to see patients who can't pay in cash

i know this may seem pointless but i cant find someone with the answer anywhere. the answer is a

[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.