devikeerthan wrote:Pedanius Dioscorides, a first-century physician and botanist, presented detailed information about medicinal materials and practices in his five-volume book De Materia Medica, a compilation of all medicine after Hippocrates and summarizing as well new experiments that Dioscorides was himself working on.

(A) a compilation of all medicine after Hippocrates and summarizing as well
(B) a compilation of all medicine following Hippocrates and also summarizing
(C) a compilation of all medical knowledge since Hippocrates as well as a summary of
(D) compiling all medicine from Hippocrates forward and also a summary of
(E) compiling all the medicine done since Hippocrates as well as his own summary of

A conjunction such as and must serve to connect PARALLEL FORMS.
A: a compilation...and summarizing
B: a compilation...and also summarizing
D: compiling...and also a summary
In these options, the two colored portions connected by and are not parallel forms.
Eliminate A, B and D.

A COMMA + VERBing modifier must serve to express an action that is CONCURRENT with the main action.
E: Pedanius presented detailed information...in his five volume book, compiling all the medicine
Here, the modifier in red implies that Pedanius was COMPILING all the medicine at the same time as he PRESENTED the finished book.
This sequence is illogical.
Clearly, the act of compiling was completed BEFORE the finished book was presented.
Eliminate E.

The correct answer is C.

Please note that and also is a valid construction on the GMAT.
For an official example, check here:
https://www.beatthegmat.com/redundancy-t280921.html

devikeerthan wrote:Pedanius Dioscorides, a first-century physician and botanist, presented detailed information about medicinal materials and practices in his five-volume book De Materia Medica, a compilation of all medicine after Hippocrates and summarizing as well new experiments that Dioscorides was himself working on.


(A) a compilation of all medicine after Hippocrates and summarizing as well
(B) a compilation of all medicine following Hippocrates and also summarizing
(C) a compilation of all medical knowledge since Hippocrates as well as a summary of
(D) compiling all medicine from Hippocrates forward and also a summary of
(E) compiling all the medicine done since Hippocrates as well as his own summary of

C

This is a question testing parallelism. Whenever we have a conjunction such as "and", "or", "but", "not only..but also", "as well as", etc., we need the things connected in parallel. Let us go through the options -


(A) a compilation of all medicine after Hippocrates and summarizing as well - "a compilation" and "summarizing" are not in parallel; "and..as well" is redundant.

(B) a compilation of all medicine following Hippocrates and also summarizing - same as A

(C) a compilation of all medical knowledge since Hippocrates as well as a summary of - this one is in parallel. The two noun forms - "a compilation of" and "a summary of" are connected in parallel using the conjunction "as well as".

(D) compiling all medicine from Hippocrates forward and also a summary of - "compiling" and "a summary" are not in parallel

(E) compiling all the medicine done since Hippocrates as well as his own summary of - same as D

Only option C connects the two elements in parallel.