Choose the best option

Sure! Here are the best options for each blank in the exercise:

1. **C. visited** - "I visited my old teacher last week."
2. **C. asked** - "My brother usually asks me for help..."
3. **A. finished** - "I finished all of my homework last night."
4. **C. started** - "Lan started learning English a few years ago."
5. **B. recovered** - "Only after she recovered from a severe illness..."
6. **A. had run** - "The children had run to bed before their parents came home..."
7. **C. had all gone** - "...Paul noticed a job advertisement while [the children] had all gone."
8. **C. walked** - "I walked..."
9. **C. left** - "I haven’t met him again since we left school..."
10. **B. witnessed** - "For the last 20 years, we have witnessed significant changes..."
11. **D. moved** - "My best friend Lan moved to England 10 years ago."
12. **B. works/is retiring** - "Mr. Pike has worked for this company for more than thirty years..."
13. **B. waited** - "While I was waiting at the bus stop..."
14. **B. had been studying** - "By the end of last March, I had been studying English for five years."
15. **B. I’ve been calling** - "I’ve been calling Alan for hours..."
16. **A. walked - asked** - "We were walking when he suddenly asked me to help him."

Feel free to ask if you need further assistance!