Why is this usage of colon right?

The previous sentence states some fruits don't respond well to 1-MCP so this is and example of that.

This came from an SAT question:

Take Bartlett pears, for instance, unless they are treated with exactly the right amount of 1-MCP at exactly the right time, they will remain hard and green until they rot, and consumers who experience this will be unlikely to purchase them again.

A) No change B) pears, for instance: C) pears for instance, D) pears. For instance,

I went through with elimination.

"A" doesn't work because the comma set means that the sentence should still make sense without the words inside the comma set.

"B" doesn't work because the clause before the colon should be independent and make sense by itself which I think it doesn't because of the comma behind "pears"

"D" doesn't work because "Take Bartlett pears." is not an independent clause.

So I chose C but B is the answer. Could someone explain why B is right and C is wrong?

Thanks

• Note that Consider this or Take this is already complete on its own. Commented Jan 13, 2017 at 11:10
• Take Bartlett pears, for instance is an independent clause, as is the clause beginning with "unless". Independent clauses are normally separated by a terminal point like a full stop (period) or a colon. Which is why B, which uses a colon, is correct. Commented Jan 13, 2017 at 11:39
• @BillJ is there a name for the ", for instance" part of B? For example is "this is not the case, however." a independent clause? Also, is "unless it is true" a independent clause? Commented Jan 13, 2017 at 11:59
• "For instance" is an adjunct, an optional element in clause structure. Semantically, it's used to for exemplification and is often replaceable with "for example", as it is in your example. Yes, this is not the case, however is an independent clause. Unless it is true is a preposition phrase, but it is sometimes found alone especially with "of course", as in Unless it is true, of course. Commented Jan 13, 2017 at 12:55

The part after the colon is supposed to express a logical outcome, elucidation, or enumeration of what went before the colon.

In your sentence, the part before the colon

Take Bartlett pears, for instance: ...

is setting up an example of a proposition (of something stated just prior to this sentence) which will be considered in the latter portion of the sentence. In fact, "for instance" is another way of saying "for example".

The rest of the sentence

... unless they are treated with exactly the right amount of 1-MCP at exactly the right time, they will remain hard and green until they rot, and consumers who experience this will be unlikely to purchase them again.

elucidates the case of Bartlett pears, describing the behavior in the example case.

You would not use C for a number of reasons, chief among them that dividing the sentence thus on the single comma forces the unless to be considered as a subordinating conjunction meaning "except on the condition that" which, in this case, would mean the following material is an exception to the proposition of which Bartlett pears are an example, not an illustration of it. Clearly, the material is intended to be an illustration.

C is wrong because "take Bartlett pears, for instance" is a full sentence, and needs to come to a conclusion with either a period, colon or semicolon, not a comma. B is correct, albeit a bit awkward. I feel like it should read "Take Bartlett pears for instance;" The comma really isn't necessary, but it technically is still correct.

You're explanation for why D is incorrect is wrong. You said ""D" doesn't work because "Take Bartlett pears." is not an independent clause." In fact, "Take Bartlett pears" is indeed an independent clause, which is precisely why it needs to be concluded with, once again, either a period, colon, or semicolon, and not a comma. To illustrate, if you replaced Bartlett pears with a pronoun, it would read "Take this.", which is a full sentence. The reason D is incorrect is not because it is not an independent clause, but because it is not concluded with a period, colon, or semicolon.