What allowed the Khmer kingdom to became great?

Question

A. Ability to produce excess rice and export it
B. Abundant mineral resources
C. Technological advances
D. Ability to conquer other lands

I have a hard time with this question. Either A or D?

Answer 1

http://www.historytoday.com/historical-dictionary/k/khmer-empire

http://en.wikipedia.org/wiki/Khmer_Empire

Read widely, including any relevant links on these pages. Let us know what you discover.

Answer 2

It mentions conquering then the wealth from the rice they would go so I'm going with D.