Why did the inca empire decline?

choose all answers that are correct.
a) the spanish were unprepared for the inca's sophisticated weapons and firepower.
b) the inca had no immunity to the disease the spanish unknowingly carried.
c) pizarro held the inca emperor hostage for a short time before freeing him.
d) a civil war weakened the inca empire before the spanish arrived.
e) the inca made the mistake of trusting the spanish to keep their word.