Writing: End-of-sentence punctuation — Harder example

which of the following would not be acceptable for now lenses are shaped in a specific way and for a very specific purpose their concentric rings amplify and concentrate light so let's take a look at these answer choices but before we do let's talk about this this word Fornell for a second because I was confused about it but my colleague who has a long history in the theater world tells me that in the u.s. you don't say the S you say it friend nel accent on the nel anyway we are trying to figure out what piece of punctuation should go between purpose and there should it be purpose semicolon there as it is in the sentence should be purpose period capital T there should it be purpose comma there or should it be purpose : there well in order to figure out what piece of punctuation we ought to use first we should evaluate what this sentence is break it down into its component parts so we've already got these aforementioned Fornell lenses well we know that this is a subject so we've got for now lenses that's our subject what's the verb that they take our okay so there's our verb are shaped and then we're gonna be looking for another noun that has a verb oh there's another one rings and then here's another verb amplify and concentrate so we've got we've got a subject verb punctuation subject verb and so what we're looking at here then is two independent clauses so I'll bracket them off so we're looking for one answer for a piece of punctuation that doesn't work all the other answer choices should be able to unite independent clauses so we're looking for the one outlier the one thing that can't do that so okay so option a semicolon what does the semicolon do it unites independent clauses so right off the bat we can say all right knock this one out we know that this works so it is acceptable we're looking for something that's not acceptable option B purpose period capital T there well so if we know that for now lenses are shaped in a specific way and for a very specific purpose is a an independent clause remember that an independent clause can also just be a that is in fact why they are independent so if this is a sentence and this is also a sentence then there's nothing wrong with dividing them up with a period and capitalizing the first letter of their so that checks out to me answer C well now this is curious we've got this comma here and we've got two independent clauses and we know that commas cannot unite independent clauses on their own they need to be combined with a coordinating or a fanboys conjunction that's the conjunctions for and nor but or yet and so and if you use a comma plus a coordinating or fanboys conjunction you can combine two independent clauses but if you don't if there's no fanboys if it's just a comma on its own that results in what we call a comma splice which is ungrammatical so right now option C is looking like it might be our choice well but let's see if we can eliminate answer choice D let's not jump to any conclusions so this one uses a : purpose : there well what are the powers of a : we know that the colon has the power to introduce things how do you do I'm the colon the colon can introduce lists rather like this one descriptions explanations or quotations and also in order to use a colon and a colon has to follow an independent clause so what we're looking at here is an independent clause connecting to another independent clause and it's not a list but it is kind of a description or an explanation for now lenses are shaped in a specific way and for a very specific purpose : their concentric rings amplify and concentrate light so it describes their shapes concentric rings and it describes why the purpose for amplifying and concentrating light we're kind of using this punctuation mark the colon as an accelerating agent right we set up in this first independent clause that for now lenses have these particular properties and then we use the colon to build momentum into the second independent clause and so what does this mean it means that we can use colons which means we can knock out this answer which means that C is our correct choice when you're given a punctuation question like this one the first thing to do is to figure out the context of the sentence you know how many independent clauses or dependent clauses are you working with because that can change the landscape and that can change the the appropriate punctuation to use in that scenario