How long should children be allowed to play in free-choice activities (centers/interest areas) before they are required to begin cleaning up? 15 minutes - where a timer is set and children rotate in the centers during the hour 30 minutes 45 minutes one hour

[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.

According to proper standing posture, from a side view, which parts of the body should be aligned? a. ear, shoulder, hip, knee, and ankle b. stomach, hip, knee, and ankle c. nose, shoulder, hip, knee d. ear, shoulder, fingers, ankle

Can someone give me a hand with this one.