Which of the following best explains the Mongolian khans’ difficulty with bringing Vietnam under the Pax Mongolica? The policy of defense and fortification to prepare villages and cities for times of war
The policy of nonviolent resistance and diplomatic negotiation, supported by Hindu religious leaders
The policy of establishing strong trade ties with the Yuan dynasty to deter a conquering force
The policy of forced labor to quickly establish a conscripted army when facing attack

The answer is A.) The policy of defense and fortification to prepare villages and cities for times of war.

Explanation:

Read this quote, ""The Chams from the time of King Wen knew the art of fortification. They protected their cities with walls in brick. The citadels and strong places served as depots for materials of war". You can see that they had to defend and fortify the village to prepare themselves for war making A the correct answer. Answer B is not correct because it doesn't mention about non violence negotiation, and also it wouldn't make sense why it was difficult to bring Vietnam under Pax Mongolica. Answer C is not correct because it didn't mention anything about the Yuan dynasty. Answer D is not correct because it didn't mention about forced labor to quickly get ready for an army when facing attack. Look for clues in the passages as you read and then you'll find the correct answer. However some questions may have 2 answers that are good but one of them is better. I hope this helps and this one of the questions I got wrong btw.