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

C) The policy of establishing strong trade ties with the Yuan dynasty to deter a conquering force.

Explanation:

Mongols use to rule by power. They were physically strong and had gained empire through brutality. Mongols wanted to rule Vietnam but they also wanted to increase trade stability. For this purpose Mongols decided to rule with peace. They had to change their nature and promoted peace during Pax Mongolica to flourish trade.

a. factors that are used to make goods and services

to act quickly in times of danger to the united states

because you have to act quickly if you want to live/survive.