Sentence Correction

Lot of times we hear that Punctuations are not part of syllabus in GMAT. It is partly "True".
Colon ":" -
Important rule to follow regarding colon is "The part of a sentence before a colon must be an independent clause".
Colon works on two rules.
The first part is able to stand alone. And the second part clarifies/simplifies the first part.
Colons can also go before explanations, rules, or examples.
Semicolon ";"-
Semicolon interconnects two independent clauses. If the Semi colon is removed, they should have concise meaning and grammar separately.
Semicolon links two closely related sentences in terms of concept/idea/feeling.
When we need to express some important linking between two independent clauses, we might join them with a semicolon.
Example: My grandfather seldom goes to bed this early; he's afraid he'll miss out on something.

We need to understand that some official questions are available on "Semicolon".

Q. Certain pesticides can become ineffective if used repeatedly in the same placeï¼›one reason is suggested by the finding that there are much larger populations of pesticide-degrading microbes in soils with a relatively long history of pesticide use than in soils that are free of such chemicals.

(A) Certain pesticides can become ineffective if used repeatedly in the same placeï¼›one reason is suggested by the finding that there are much larger populations of pesticide-degrading microbes in soils with a relatively long history of pesticide use than in soils that are free of such chemicals.

(B) If used repeatedly in the same place，one reason that certain pesticides can become ineffective is suggested by the finding that there are much larger populations of pesticide-degrading microbes in soils with a relatively long history of pesticide use than in soils that are free of such chemicals.

(C) If used repeatedly in the same place，one reason certain pesticides can become ineffective is suggested by the finding that much larger populations of pesticide-degrading microbes are found in soils with a relatively long history of pesticide use than those that are free of such chemicals.

(D) The finding that there are much larger populations of pesticide-degrading microbes in soils with a relatively long history of pesticide use than in soils that are free of such chemicals is suggestive of one reason, if used repeatedly in the same place, certain pesticides can become ineffective.

(E) The finding of much larger populations of pesticide-degrading microbes in soils with a relatively long history of pesticide use than in those that are free of such chemicals suggests one reason certain pesticides can become ineffective if used repeatedly in the same place.

Answer :
(A) Can not lay hands on this choice. The topic is split with a semicolon, a sensible thing to do in such cases.

(B) The participial modifier - If used repeatedly- should modify pesticides and not one reason

(C) The participial modifier - If used repeatedly- should modify pesticides and not one reason

(D) The sentence is a run -on. The second part of the topic, going after - if used repeatedly - is dangling loosely without a connector such as that or a semicolon. Hence, wrong

(E) As in D, a connector as -that- is essential between reason and certain.
Hence A is the Right Answer.
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