When waging war in China, the Mongols faced which challenge?

Question $49$ options:

Many Mongol soldiers were Buddhists, and so they were reluctant to engage in violence against the Chinese because many of them were also Buddhists.

Chinese cities were usually walled, and some of these walled cities even connected to smaller fortified towns through a set of underground tunnels.

The Chinese employed camel$-$mounted soldiers. These camels could go even further without water than horses, and so could outmaneuver Mongol troops when fighting them in the Gobi Desert.

The vast swamps of Northern China meant that the Mongols were unable to use their cavalry for mobility, depriving them of one of their key advantages.