An independent clause and a dependent clause.
An independent clause is a clause that can stand alone as a sentence (i.e., it expresses a complete thought). However, a dependent clause (or subordinate clause) is one that cannot stand alone as a complete sentence because it does not express a complete thought. Cause it is not a complete thought, it is dependent on being attached to an independent clause to form a sentence. The link between a dependent clause and an independent clause will often be a subordinating conjunction or a relative pronoun.
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I don’t understand what you’re trying to ask?
Even though you didn't give us the fragment with the comma slice, it isn't really necessary here as we can answer just based on these 4 options here. All options apart from the second one are correct - only the second option doesn't fix the mistake of the comma splice, whereas the other options do but connecting the sentences properly.
