How are health science professionals like educators? I only need one reason. Thanks so much if you can help.

What a self improvement for a busy person who had difficulty finding time to exercise/ dropping out of clubs and activities/ refusing social invitations from friends/ scheduling daily invitation activity/ sleeping fewer hours at night

[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.

Why would one lymph node in the neck be swollen and not the other? what causes them to swell?