Alexander Was Successful in Conquering Much of Persia Because

Alexander was successful in conquering much of Persia because:

A) the Macedonian army was much larger than the Persian army.
B) Macedonians were more fierce warriors than the Persians.
C) he was a better military tactician than Darius III, emperor of Persia.
D) Darius III of Persia had underestimated the threat Alexander and his army posed.
E) Alexander engineered a stealth invasion so the Persians did not know they were coming.