Which of the following is a compound sentence?

• Compound sentence:- A compound sentence is a sentence that connects two independent clauses, typically with a coordinating conjunction like and or but.- They're best for combining two or more self-sufficient and related sentences into a single, unified one.- Compound sentence এ একের অধিক principal clause থাকে যাদেরকে co-ordinate clause বলা হয়।• অর্থাৎ Compound sentence এ দুই বা ততোধিক principal clause বা co-ordinate clause থাকে।- এছাড়া Compound sentence এ সাধারণত and, or, but, yet, so, therefore, otherwise, else, both and, either --- or, neither nor, not only --- but also ইত্যাদি co-ordinating conjunction দ্বারা দুইটি principal clause যুক্ত থাকে।• সুতরাং, অপশনে উল্লিখিত বাক্যগুলোর মধ্যে-- অপশন খ)- She studied hard but failed the test হচ্ছে Compound Sentence.- অপশন ক) হচ্ছে Simple Sentence এবং অপশন গ) এবং ঘ) হচ্ছে Complex sentence.Source: Advanced Learner's by Chowdhury & Hossain.