Which of the following countries is on the best terms with North Korea and has demonstrated this in their treatment of 2010 events concerning disputes (sometimes violent) between North and South Korea over maritime boundaries?

Hi,

The answer is China

Over time, China has demonstrated their support to North Korea. In 2010 North Korea attacked with artillery the island of Yeonpyeong, where there were civilians, and South Korea responded by attacking North Korea's artillery.

Tensions scaled, and although most world governments condemned the attack, China's Ministry of Foreign Affairs didn't explicitly condemn the bombarding by North Korea and only made a call to peace in the Korean Peninsula.