One reason HIV/AIDS is serious is a. the virus survives well in the environment.
b. it is transmitted through casual contact.
c. many infected people do not know they are infected.
d. people do not know how to prevent it.

help please

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.