Vaccination has proven to be a highly effective weapon against certain diseases. –, which at its peak in the 1940s and 1950s infected – in the United States each year, has been – eradicated worldwide through vaccination. Newly developed vaccines against diseases such as – hold great promise as a public health tool in Africa.

Check all that occur during ventricular systole. a. the av valves open to allow blood to enter the ventricles from the atria. b. the av valves open to allow blood to enter the ventricles from the atria. c. the semilunar valves remain closed throughout systole to prevent backflow of blood into the ventricles. d. the semilunar valves remain closed throughout systole to prevent backflow of blood into the ventricles. e. the semilunar valves open to allow blood to flow into the large arteries. f. the semilunar valves open to allow blood to flow into the large arteries. g. the av valves close to prevent backflow of blood into the atria.