Sentence Correction

Each of the factory owners that felt that pollution was a severe problem wanted a drastically reformed system of industrial waste disposal in the area.
(A) owners that felt that pollution was a severe problem
(B) owners which felt that pollution was a severe problem
(C) owners who felt that pollution was a severe problem
(D) owners who felt that pollution to be a severe problem
(E) owners, feeling that pollution was a problem quite severe,

[spoiler]1. Why is D wrong,
2. should not there be a "is" in place of "was" in C.
OA:C[/spoiler]

Each of the owners refers to a singular person so in this case who is the correct pronoun.

felt that to be is not idiomatic. Is should not be used as the sentence Each of the factory owners that felt that is in past tense. So the usage of 'is' is wrong.

So C should be the answer.

Can you please explain more:
isnt it like: the owners felt that pollution is a problem. (we indicated past by using 'felt')

is it wrong :
I thought i am prepared ....in the past i thought i am prepared
I thought i was prepared ( this is passive, what is its active counterpart)

Each of the factory owners that felt that pollution was a severe problem wanted a drastically reformed system of industrial waste disposal in the area.
(A) owners that felt that pollution was a severe problem - that is wrongly refers to owners
(B) owners which felt that pollution was a severe problem - which is wrongly refers to owners
(C) owners who felt that pollution was a severe problem - who refers to each of the owners and was is used
(D) owners who felt that pollution to be a severe problem - to be is wrong here, past tense is required since wanted is also in past tense
(E) owners, feeling that pollution was a problem quite severe, - a relative pronoun is required to refer to owners

C correct usage of relative pronoun who here.

reporting verb is felt a past participle format.Thus 'was' is a correct usage.

IMO B is the right answer.
In C, 'felt pollution to be' is wrong due to tense inconsistency.