Which best describes the mood of the story?
a) secure
b) intense
c) certain
d) upbeat

b

explanation:

It is false that during exercise, the oxygen concentration in the blood increases to twice that of resting levels. As a matter of fact, the oxygen either stays the same or decreases, or it may increase slightly than it used to be when the person was resting, but it definitely does not double while exercising. Hope this helps. Let me know if you need additional help!