Renaissance sentence correction

[sirisha.g]

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) doubted that Troy had ever existed
(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

Could someone explain why C is wrong.

[gmatmachoman]

Pick A.

Original sentence is correct as it's the verb tense (past perfect tense) properly incorporates the "time shift".

[reply2spg]

Though I choose D, I feel A is correct. I completely missed 'had' in A.

Since you have 'by the eighteenth century' you need 'had'. This concept is very well explained in e-gmat

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) doubted that Troy had ever existed
(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

Could someone explain why C is wrong.

[indiantiger]

A , only logical choice