In Some Industries, Pollution Rights Are Sold from One Company

In some industries, pollution rights are sold from one company that does not need them to another that does. In recent years, conservation groups have purchased pollution rights so they cannot be exercised. Companies in need of pollution rights would find that:

A) the supply of pollution rights had increased.
B) the prices of pollution rights had fallen.
C) the relative costs of pollution control equipment had gone up.
D) the relative costs of pollution control equipment had fallen.