Sentence Correction

The insect, famed for its remarkable annual migrations, faced declines in habitat on both the Central American and Canadian ends of its range for decades, now is the focus of an urgent push for a rescue.


decades, now is the focus of an urgent push for a rescue


decades, has now become the focus of an urgent rescue push


decades, and now is the focus of an urgent push for a rescue


decades now, is the focus of an urgent push for a rescue


decades; now is the focus of an urgent rescue push

{A} - Incorrect: it's an run on sentence.
{B} - Incorrect: we need "and"
{C}
{D} - Incorrect: we need "and"
{E} - Incorrect: the part after semicolon is not clause.

{C}???

Hey shibsriz,
This sentence features a couple of issues; let's spot and take care of them.

A) Good example of the so called "run-on" sentence. A "run-on" sentence has two independent clauses; it is a structural flaw that is fixed with the introduction of a subordinator to properly connect the two sentences. In particular, when two independent clauses are connected only by a comma the ensuing "run-on" structure is called "comma-splice".
B) Same error here. We need a conjunction to connect those clauses.
C) Comma-splice issue has been fixed, moreover there's a neat parallelism. Correct.
D) The word "now" is in the wrong place and conveys a skewed meaning. Comma-splice error.
E) The use of semi-colon corrects our comma-splice issue, but what should follow the semi-colon is a full clause not a fragment. Thus this one is incorrect.

Hope it helps,
-tathastuGMAT