Which of the given characteristics describe parabolas that open up?

When all the values in a data set are written in order from least to greatest, the value that is in the middle, with an equal number of values below it and equal number of values above it, is called the .

Whic disease reduces bone density and causes the bones to become brittle

[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.