Must compare like things and you are given owners in the non-underlined portion of the sentence. Therefore, eliminate A,B, and D. C is the correct answer because dwelling should be plural and in choice E, it is not. C is concise and clear and the meaning makes sense.

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"owners of condominium apartments have" is parallel to "owners of cooperative apartments have". Whereas is used to express contrast.
Hence C is the correct answer

"Whereas" is used to show contrast.
"While" gives the idea of "at the same time".
(A), (B) and (E) are eliminated for this reason.
In (C), "Whereas" is modifying the entire clause and is correct. (D) is wrong for the same reason.

Official Explanation :

Choices A, B, and D can be faulted for comparing a single owner of a condominium with owners of cooperative apartments.

In choice C, the best answer, the nouns agree in number.

Nouns also agree in choice E, but one cannot tell whether the title or the dwelling is said to be free and clear.
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While the owner of a condominium apartment has free and clear title to the dwelling, owners of cooperative apartments have shares in a corporation that owns a building and leases apartments to them.

(A) While the owner of a condominium apartment has free and clear title to the dwelling,

(B) The owner of a condominium apartment has free and clear title to the dwelling, but

(C) Whereas owners of condominium apartments have free and clear title to their dwellings,

(D) An owner of a condominium apartment has free and clear title to the dwelling, whereas

(E) Condominium apartment owners have a title to their dwelling that is free and clear, while

To maintain parallelism while comparing two subjects, it is essential to make sure they are similar.
In this case, the latter part of the sentence has the subject "owners of cooperative apartments".
So, we want to make sure the first part of the sentence also has a plural comparable subject.
(A), (B), (D) are gone.

Between (C) and (E), (C) has even better parallel structure. Whereas "owners of" ... , "owners of" ...

Ans: (C)

While the owner of a condominium apartment has free and clear title to the dwelling, owners of cooperative apartments have shares in a corporation that owns a building and leases apartments to them.

(A) While the owner of a condominium apartment has free and clear title to the dwelling,

(B) The owner of a condominium apartment has free and clear title to the dwelling, but

(C) Whereas owners of condominium apartments have free and clear title to their dwellings, --> correct

(D) An owner of a condominium apartment has free and clear title to the dwelling, whereas

(E) Condominium apartment owners have a title to their dwelling that is free and clear, while

daagh can you please brief the difference between dwellings and dwelling in C and E ?

teaser
'dwelling' is not correct in the given context. Each owner has his own dwelling and as such. all owners have their own dwellings. Otherwise, it looks as if all owners have one single title and one dwelling in E.

These are more contextual than formulaic.

At the same time, we can use the singular in spite of the plural subject. As in the following case, we say that all MDs have their own say in the conduct of the company and not their "says" (plural of say)
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The clue lies in non-underlined portion of the sentence
The last word "them" truly refers to the owners of the condominium.
On this basis eliminate A, B, and D for the singular "owner"

E looks crapy, clear and free is the title not the dwelling

Circle C and have a nice day

A, B, and D - comparing a single owner of a condominium with owners of cooperative apartments.
E -one cannot tell whether the title or the dwelling is said to be free and clear
C - the best answer, the nouns agree in number.

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