For gas exchange to be efficient, the respiratory membrane must be
a. between 5 and 6 micrometers thick.
b. at least 3 micrometers thick.
c. 0.5 to 1 micrometer thick.
d. the thickness of the respiratory membrane is not important in the efficiency of gas exchange. 4 points

Andrew feels good about himself. he doesn't know exactly why he is so happy, but every day he looks forward to his schoolwork and chores. "i play a game," he says. "i make a list of everything i have to get done, and then i try to finish it all before a certain time. for some reason, i feel great when i beat my time." based on this information, why is andrew happy? he gets a proper amount of sleep he eats healthy meals he has a strong family support group he regularly meets his own goals