Earth is a closed system. that means the amount of rocks, metals, carbon, nitrogen, oxygen, and water on earth so it is essential that bio geochemical cycles __ these materials as they move through earths subsystems
a: remains constant. can increase. can decrease.
b: destroy. create. renew.

The Earth is a "closed system" which means that the amount of rocks,  carbon, metals, nitrogen, water and oxygen on earth remains constant. So it is essential that "biogeochemical cycles renew these materials" as they move through the Earth's subsystems.

Explanation:

The Earth's only source of extra-planetary energy is the Solar radiations received by Earth. The biogeochemical cycles on the planet are responsible for processing the same old rocks, metals, carbon, nitrogen, oxygen, water, and other abiotic substances on Earth in order to naturally renew them and make them available for reuse. No naturally occurring element on Earth is newly produced. It is only renewed through biogeochemical processes.

What type of link is

Answer after wwii, communist countries in eastern europe formed the warsaw pack, a military alliance, and comecon, an economic alliance;