With which belief system is the yin-yang circle associated?

Taoism is the correct answer.

Explanation:

The Yin Yang circle is also known as the Tai Chi symbol. It is a circle which is is divided by a curved line into two halves. The black part represents the Yin side, while the white part reflects the Yang side. A dot is in the center of both the halves. It has its roots in Taoism, which is Chinese religion and philosophy. The black half is associated with shadows and femininity, the white side is associated with brightness and growth.

c it says nothing about connecting those 2 seas.

protected civil liberties and outlawed slavery in the new territories.