The comma before "And" does not necessarily suggest that the last item in the parrallel list be "Independent clause"

AND - is used to join entities

X, & Y - If X is IC then Y needs to be IC to maintain parallelism.

In this case, X,Y, Z, & A - The last element is not parallel with the remaining 3 elements. The last element is out of sync. So, it needs to be removed.

The correct option (C) - does the same. X - Have reduced sickness , Y - Have reduced sleeping, Z - Have reduced fatigue,
A - contrast (represented by While) - Raising production efficiency.

Recently implemented "shift-work equations" based on studies of the human sleep cycle have reduced sickness, sleeping on the job, fatigue among shift workers, and have raised production efficiency in various industries.

(A) fatigue among shift workers, and have raised

(B) fatigue among shift workers, and raised

(C) and fatigue among shift workers while raising

(D) lowered fatigue among shift workers, and raised

(E) and fatigue among shift workers was lowered while raising

Illustration: When we provide a list of items using commas we must maintain the
following structure.
A, B, C and D.
This is a proper parallel structure concerning items in a list, and this structure needs to be maintained in a clause. Another thing of importance in this sentence is the contrast that is presented.

GMATNinja , egmat , VeritasKarishma , MartyMurray

I am finding it difficult to accept C as the answer choice. As per my understanding, "while" is a subordinator and required a bonafide verb which is clearly missing here in option C. Can anybody please help me understand?

Hi there,

Recently implemented "shift-work equations" based on studies of the human sleep cycle have reduced sickness, sleeping on the job, fatigue among shift workers, and have raised production efficiency in various industries.

There is no problem in the parallelism of the entities in the list because all the three entities are noun entities are grammatically parallel.

Yes, “sleeping on the job” is a gerund – a noun that denotes an action. However, “sickness” and “fatigue” are not Concrete Nouns. They are “Abstract Nouns”.

By definition, Concrete Nouns are those nouns that are perceivable through five senses whereas the Abstract Nouns are those nouns that can only be experienced or felt.

There is no problem in a gerund being parallel to other abstract noun phrases. Frankly speaking, we need not even get to these grammatical complications of these entities.

Remember, this is an official question. These entities, at least “sickness” and “sleeping on the job”, are in the non-underlined portion of the sentence. Hence, rather than asking whether usage is correct or not, we must learn such usages from these sentences as they ARE correct.

Also, “raising production…” is not a verb. Note that the verb-ing word by itself cannot be a continuous/progressive verb. It must be preceded by such helping verb as is/am/are/was/were etc. to function as a verb. For example:

1. I am writing a letter.
2. He was playing soccer.
3. They are going to school.

Hence, in the correct answer choice, there is just one verb – “have reduced”.

e-gmat concept Parallelism – Helpful Tips lists out the entities that can be parallel and that cannot be parallel.

Hope this helps.
Thanks.
Shraddha