Mark the statements correctly if it correctly identifies or explains methods genghis khan used to gain power and enlarge his empire.

a: used terror as a weapon and an effective war tactic.
b: gave the inhabitants of cities he attacked the choice of surrendering or dying
c: put away his soldier's armor and ruled as emperor
d: used new fighting methods including siege towers, scaling ladders, and catapults
e: turned his warriors into an army and united the mongols
f: commanded his soldiers to fight pretend battles to sharpen their skills