Answer: 4) Correct sentence.
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Explanation:
There are no grammatical errors with the sentence.
The comma separates the dependent clause from the independent clause. The dependent clause needs the independent clause, or else the sentence wouldn't make much sense. The "if you look through the window" all on its own is missing a resolution of sorts to the statement. However, "You can see the mountain peaks in the distance" is a complete thought that doesn't need any other piece to complete it.
We don't have a run-on sentence because the sentence is fairly short. Run-ons tend to be long-winded and go on for quite a while. There isn't any hard fast rule (in my opinion anyway) but you'll know when you see a run-on.
A fragment is effectively the opposite of a run-on. It's something that's too short and missing a key element to make it a complete sentence. "If you look through the window" is an example of a fragment.
A comma splice is where you put a comma when you should have used a period. So comma splices occur when you join two sentences with a comma, when they should just be two separate sentences. An example would be: "I went to the store today, there was a long line at the checkout counter". The fix would be "I went to the store today. There was a long line at the checkout counter". We don't have a comma splice going on with the original sentence, because the first part is not a full sentence on its own.
In short, we can rule out choices 1, 2, and 3, leaving us with 4 as the correct answer. The given sentence has the correct grammar.
