Question on picture plsss help

[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.

Wich technque is not recommended for use as a supporting detail

What is the main goal of recommended dietary allowances (rdas)? to inspect school cafeterias across the united states to regulate foods sold at supermarkets and farmers' markets to investigate claims of tainted food being served in restaurants to indicate daily nutrient requirements