At the beginning of the twentieth century, Edward Stratemeyer was advertising for writers to help him—
people not only who could write children's mystery books for his popular syndicate, but mimicking his successful formula also in order to continue the many series he had begun but was too busy to continue.
A. people not only who could write children's mystery books for his popular syndicate, but mimicking his successful formula also in order to continue ---
The modifier part is not parallel. ‘People not only who could write’ should be matched by a parallel “people or those who could mimic. B. people who could not only write children's mystery books for his popular syndicate but also mimic his successful formula in order to continue the many series he had begun but was too busy to continue –
This is the answer. C. someone who not only could write children's mystery books for his popular syndicate, but also to mimic his successful formula in continuing –
one can’t say write in the plural and then ‘someone’ in the singular D. that being people who could not only write children's mystery books for his popular syndicate, but mimicking his successful formula for continuing –
being is wordy and superfluous and is a modifier of the demonstrative pronoun ‘that’. One can’t even guess what ‘that’ stands for --- wrong E. being people not only who could write children's mystery books for his popular syndicate, but mimic his successful formula also, continuing –
‘being’ is wordy and superfluous.