Giúp mình với! ( giải thích vì sao luôn)

Here are the answers: I. Identify each sentence as either simple (S) or compound (C). 1. Kelvin and Frank took the bus. (S) 2. He likes coffee, and she likes tea. (C) 3. My sister and I want to study in the morning. (S) 4. Will Brian go, or will Jimmy go? (C) 5. John rode his bike and skated this Sunday. (C) 6. Tommy likes Jodie; however, Jodie doesn't like Tommy. (C) 7. We waited for the bus, but it was late. (C) 8. Many students like to use smartphone after school. (S) 9. Although the sun is shining, it isn't very warm. (C) 10. Salad is cheap; moreover, it's very healthy. (C) II. Match the clauses to make compound sentences. 1. I hate fast food; or should I wait until next month? 2. The students missed the bus, so they took a Grab car. 3. He studied hard for the exams; yet he has never understood her. 4. He has known her for a long time, however, I love sandwiches. 5. Stop singing karaoke too loud; otherwise, I'll call the police. 6. Should I take the IELTS test this week, or should I wait until next month? 7. They hired a seven-seat car; however, it was still too small for their family. 8. If you go out without a raincoat now, you'll surely get wet. 9. He should turn himself in to the police; otherwise, he will receive heavier punishment. 10. Her calculations were right; however, her assumptions were wrong. III. Choose the best answer to complete the sentences. 1. This is good coffee; it's made locally. (D. and) 2. The cinema tickets were sold out, so we couldn't watch the movie. (B. so) 3. Chemistry is such a difficult subject; nevertheless, I enjoy learning it. (A. nevertheless) 4. She owned a motorbike, yet she didn't know how to drive it. (C. yet) 5. I could not find my pencil because it was covered by the books. (A. because) 6. Unless students do not know how to start the experiment, the teacher will give step-by-step instructions. (C. Unless) 7. I'll have a week in Da Nang, so I'll go to Hoi An for three days. (D. but)