What are contour lines on a contour map

a.lines above and below the equator
b.lines that run from the north pole to the south pole
c.lines that connect meridan
d.lines that connect points

D.

contour line of a function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value.

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!