Which one of the following measures how well your heart gets oxygen-rich blood to all your muscles while you’re exercising?

a. metabolism

b. muscular endurance

c. endorphins

d. cardiorespiratory endurance

So i have a lot of answers answered but it says i still need to answer more questions. why is it doing that? how many questions need to be answered?

What are possible signs and symptoms of drug addiction? check all that apply. declining physical appearance and health failing to meet family, school, or work obligations needing less and less of a drug to get the same effect using drugs when there is no health benefit failing in attempts to stop using a drug stealing to get drugs

Mucous membranes.. a. cover or line external surface of body. b. line internal body surfaces that are in contact with the environment. c. produce antibodies to combat infection. d. secrete sweat, which has antibacterial enzymes.