Among the Most Surprising Aspects of Mongol Rule, Given the Way

Among the most surprising aspects of Mongol rule, given the way in which they conquered and subdued various peoples, was that

A) they usually deferred to those they had conquered once they had settled in.
B) their periods of rule are often described as "peaceful" and "benign."
C) their control waned as quickly as it had waxed.
D) both a and b
E) both b and c