How and why did Ming China isolate themselves in the late 15th century?

This was done so as to focus on the inward development of the country

Explanation:

The Ming Dynasty ruled China between the Yuan and Qing Dynasties from 1368 until 1644. During this period, the ruling Emperors of the Ming Dynasty   decided to isolate China from foreign influences so as to focus on the inward development of the country. The Chinese at that time already had enough technology and did not have need for resources from other countries.

the answer is b for brother