What river forms the border between china and the korean peninsula

Amnok / Yalu

Explanation:

The 493 miles (795 km) Amnok/Yalu river forms most the border between China and North Korea, on the Western side of the border.  The rest, to the East, is formed by a shorter river named Tumen,

The name Yalu is used by the Chinese people, while the people from North Korea use Amnok or Amrok. It's a very shallow river, the deepest point is about 8 feet (2.5 m), but it has been used as natural border for centuries.

b.

developed countries have tended to improve the environment, while developing countries have tended to damage it.

(4,-2)

explanation:

6x+4y=16

-6x-9y=-6

-5y=10

y=-2

x=4