Final answer:
The properly punctuated sentence uses commas to correctly separate a dependent clause and connect two independent clauses within a compound sentence.
Step-by-step explanation:
The sentence that is properly punctuated is: "Although I prefer English, I know that math is important, and I will work hard in both classes." This sentence correctly uses a comma to separate the dependent clause at the beginning from the independent clause that follows. It also correctly uses a comma before the conjunction 'and' to connect the two independent clauses that make up the compound sentence. Proper punctuation is critical for clarity and meaning in writing.