Most environmental problems can be traced to three underlying causes; the number of humans on this planet, utilization of resources at a very fast rate and

Pollution

Most environmental problems can be traced to three underlying causes; the number of humans on this planet, utilization of resources at a very fast rate and pollution.

Pollution is the contamination of the environment by the introduction of any substance (pollutants) which may be liquid, solid or gaseous that makes the environment dirty and unhealthy. The major types of pollution include land pollution, water pollution, and air pollution. Others include noise pollution and light pollution.

answer; ///(b) it is composed of four protein chains and four heme groups;

i think the answer is b.