Levees and embankments allow humans to
a. conserve water supplies
b. produce hydroelectricity
c. settle below river level
d. transport resources

Levees and embankments allow humans to c)settle below river level. A levee is defined as "an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels." This definition can also be used for the term embankment.

The answer is the magnetosphere.

Here is a picture  of the net. its 4 squares in a row diagonal and on the third draw one square aove and under