The industrial pollutants known as PCB's were first manufactured in 1929 and were used as coolants for electrical equipment in Europe and North America until the 1970s, when studies showed that the compounds had entered the food chain and were harmful to some animals.
(A) that the compounds had entered the food chain and were harmful to some animals
(B) the compounds to have entered the food chain and be harmful to some animals
(C) the entry of the compounds into the food chain as harmful to some animals
(D) the entry of the compounds into the food chain and its harmfulness to animals
(E) the compounds entering into the food chain and harming some animals
(A) that the compounds had entered the food chain and were harmful to some animals
(B) the compounds to have entered the food chain and be harmful to some animals
(C) the entry of the compounds into the food chain as harmful to some animals
(D) the entry of the compounds into the food chain and its harmfulness to animals
(E) the compounds entering into the food chain and harming some animals
This sentence is actually pretty simple.
