Campaign speech writers are the engine that powers political campaigns, dissecting issues and not oversimplifying them, as in campaign commercials.
Let's choose which of the GMAT errors the sentence has:
1. Rhetorical Construction
2. Parallelism
3. Diction
4. Verb Form
5. Agreement
6. Grammatical Construction
7. Logical Predication
8. Idiom
Logical Predication, Grammatical Construction
Logical predication is tested when Campaign speech writers are compared to campaign commercials as in
choices B and E.
Grammatical Construction is tested when we have to choose between 'dissect' and 'and dissects'.
Common error one can make in this is understand this question to be a parallelism tester and end up choosing 'and dissects' which SOUNDS parallel to 'engine that POWERS'.
AND Usage:
and is a coordinating conjunction (Coordinating conjunctions connect words, phrases, and clauses.) and it always presents a non contrasting item ('presents non-contrasting item(s) or idea(s) ("They gamble, and they smoke.")) from wikipedia.
Why we should choose 'dissecting'?
Dissecting is the present participle of the verb 'to dissect'. If used here, it correctly describes an action that happens at the same time as the action in the main clause (which states that campaign speech writers 'ARE' the engine that powers...)
Having said all the above lets see each answer choice:
A.dissecting issues and not oversimplifying them, as in campaign commercials - INCORRECT - Comparison is not correct, campaign writers are engine that powers..dissecting issues.. as in campaign commercials. A verb is missing, 'as is done in campaign commercials' could have been a better comparison.
B.dissecting issues instead of oversimplifying them, like campaign commercials - INCORRECT - Speech writers actions are compared to campaign commercials - verb compared to noun - commonly found error in logical predication SC's
C.dissecting issues rather than oversimplifying them, as campaign commercials do - CORRECT - Verb form and comparison is appropriate and has no errors. (I found that later clause 'as campaign commercials do' seems to refer to entire previous clause, sounding like campaign commercials also dissect issues rather than oversimplify them. But then, we don't have any choice which has this error removed except E, which is error prone because of usage of 'and dissects' which does not agree with plural verb..
D.and dissects the issues but does not oversimplify them, as is done in campaign commercials - INCORRECT - Subject verb disagreement - Campaign speech writers is plural and 'does not' must be used with singular, similarly 'and dissects' is for singular.
E.and dissects the issues, unlike campaign commercials that oversimplify them - INCORRECT - Same error as above.
IMO this can be a sufficient enough explanation. Let me know if you need more clarity on any stuff i mentioned.
