Why did proponents of the torture memo believe that waterboarding was an acceptable interrogation technique?

A.
They argued that waterboarding was used in multiple conflicts throughout the twentieth century.
B.
They argued that waterboarding was not considered torture in countries like Iraq, so could be used by the United States.
C.
They argued that the president had the authority to do whatever he deemed necessary to get information in the global war on terrorism.
D.
They argued that Congress had not specifically outlawed waterboarding, so it should be upheld as a useful tactic.