What is cardio endurance

i only need like a little answer 7th grade

The germs that cause infections are mainly spread in what three ways? a. immunization, mucous membranes, not washing hands b. germ-laden droplets, direct contact with body fluids, insects c. hand hygiene, sickness, immunization d. not enough sleep, low oral hygiene, germs

Blood cells bring oxygen to cells and take carbon dioxide away. true or false

[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.