Official Solution:
The marketing expert stated that it is not only the price that is offered while entering the market, but also at what speed goods are rolled out in the market that determines the success of a marketing campaign.
A. it is not only the price that is offered while entering the market, but also at what speed goods are rolled out in the market that determines the success of a marketing campaign.
B. it is not only the price that is offered while entering the market, but also the speed at which goods are rolled out in the market, determines the success of a marketing campaign.
C. not only the price that is offered while entering the market, but also the speed at which goods are rolled out in the market determines the success of a marketing campaign.
D. what determines the success of a marketing campaign is not only the price that is offered while entering the market, but also how fast goods are rolled out in the market.
E. the success of a marketing campaign is determined not only by the price that is offered while entering the market, but also how fast goods are rolled out in the market.
A. Parallelism is lost in the construction “not only (the price)..., but also (at what speed)”. The first item is a noun, whereas the second is a prepositional phrase.
B. Here “it” is a placeholder and hence must be referred to by a “that” clause or an infinitive. The correct construction here is “it is X that determines Y.”. In this option “that” is missing before the verb “determines”. Thus, the two verbs “is” and “determines” have “it” as their subject and the verbs are not joined by any conjunction.
C. Correct. Parallelism is maintained in the “not only (the price), but also (the speed)”. Both are nouns.
Moreover the structure “not only X, but also Y determines….” is correctly set up. It is to be noted that an additive, such as “not only…”, does make the subject plural - here the singular subject “the speed” correctly agrees with the singular verb “determines”.
D. Parallelism is lost in the construction “not only (the price)..., but also (how fast..)”. The first item is a noun, whereas the second is an adverbial phrase.
E. Parallelism is lost in the construction “not only (by the price)..., but also (how fast..)”. The first item is a prepositional phrase, whereas the second is an adverbial phrase.
Answer: C