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.
B. The continents on a map looked like they fit together.
A is the theory he proposed <em>after</em> making this observation
C and D would disprove his theory, not support it.