The lower part of the Hudson River contains large amounts of polychlorinated biphenyls (PCB's) and heavy metals. Which statement best explains their presence in the river?

A. They are introduced by environmentalists to kill
sewage bacteria.

B. They are the decomposition products of river organisms.


C. They were accidentally spilled into the river by fishermen.

. D. They were discharged into the river as manufacturing by-products,

Which one is the correct answer