Sentence Correction

Europeans have long known that eating quail sometimes makes the eater ill, but only recently has it been established that the illness is caused by a toxin present in the quail’s body only under certain conditions.
(A) Europeans have long known that eating quail sometimes makes
(B) Europeans have long known quail eating is sometimes able to make
(C) Eating quail has long been known to Europeans to sometimes make
(D) It has long been known to Europeans that quail eating will sometimes make
(E) It has long been known to Europeans that quail, when it is eaten, has sometimes made

IMO A .. Others contain S-V errors

Europeans have long known that eating quail sometimes makes the eater ill, but only recently has it been established that the illness is caused by a toxin present in the quail’s body only under certain conditions.
(A) Europeans have long known that eating quail sometimes makes
(B) Europeans have long known quail eating is sometimes able to make
(C) Eating quail has long been known to Europeans to sometimes make
(D) It has long been known to Europeans that quail eating will sometimes make
(E) It has long been known to Europeans that quail, when it is eaten, has sometimes made .. Awkward

Yes, A. Here europeans are not the subject, but the eater. Hence makes fits the sentence

IMO -- A

why C is wrong. C has no grammar error

C is differing the meaning of the sentence.