An item on PSAT 1:
They know it as colony collapse disorder (CCD), this phenomenon will have a detrimental impact on global agriculture if its causes and solutions are not determined.
A) NO CHANGE
B) Known as colony
C) It is known as colony
D) Colony
Choice A is wrong because it’s a comma splice.
Choice B is correct.
Choice C is wrong because it’s a comma splice, too.
Why is Choice D wrong?
I think it’s wrong because “colony” is a noun that lacks a noun “slot” (or function) in the sentence: it’s not a subject; it’s not an object; it’s not a complement. It’s nothing, really. At least, it’s nothing in terms of the sentence.
Is there a different way to see it?
Catherine & Katharine 
D is weird because it makes CCD sound like a noun of direct address.
OR, that it’s the subject, and what follows is an appositive, but your eyes roll along and realize eventually you’ve been hoodwinked and you have to recast the entire sentence meaning in your head.
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It would work as an appositive if you rearrange the sentence thusly: “This phenomenon, colony collapse disorder (CCD), will have…”
But “Colony collapse disorder (CCD), this phenomenon will have…” just sounds weird. Sometimes you can put the appositive first, as in “A man of many talents, my brother can tie shoelaces with his toes.”
I think perhaps the reason the sentence formed by (D) sounds weird is that you’re basically defining the appositive, and it’s not a phrase that people already know.
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