Which four of these developments were made under mongol rule during the pax Mongolia

They established a postal system

the spread of weapons used with gunpowder

the extension of the grand canal in China

the invention of new medicines

Explanation:

Pax Mongolica means he Mongol Peace,s the name historians have given to the time from the 13th to the 14th century when most of Eurasia was under Mongolian rule. Eurasia was unified under the Mongolian Empire and many towns and cities left with no reason to go on war with each other, so the Mongols enforced a policy of free trade. They also built the roads required to conduct this trade and then used their forces to defend the roads from bandits. Such advances have sought to create a range of innovations and inventions of global significance, such as shipbuilding methods, printing presses, the compass, and a worldwide postal system.

in all honesty, it really hasn't. except that hitler killed himself.