Sentence Correction

Q1. Cooperative appartment houses have the peculiar distinction of being dwellings that must also operate as businesses.

A. Of being dwellings that must also operate as businesses.
B. Of dwellings that must also operate like businesses.
C. that they are dwelling that must operate like as businesses.
D. that, as dwellings, they must also operate like businesses.
E. to be a dwelling that must operate as a business.

Doubt: "That" is genrally used for singulars but here in the answer it is used for "dwellings". Why so?

Q2. During the Renaissance, scholars were uncertain as to the location of Troy, and by the eighteenth century many historians doubted that Troy had ever existed.

A. Same as in sentence
B. doubt that troy has ever existed
C. were in doubt as to the existence of troy
D. were doubtful concerning troy's existence
E. had doubts about troy's ever existing

Doubt: Why C is incorrect?

Q3. It may be another fifteen years before spacecraft from Earth again venture to Mars, a planet now known to be cold, dry, and probably lifeless.

A. Same as in sentence
B. venture to Mars again, a planet now known for being
C. will venture to Mars again, a planet now known as being
D. venture again to Mars, a planet that is known now to be
E. will again venture to Mars, a planet known now as being

Doubt: Why E is incorrect.

Answers: Q1 A Q2 A Q3 A