Here are the correct answers for the numbered blanks based on the context of the advertisement/announcement:

**WHAT TO DO DURING DISASTERS**
- Question 17: **D. away**
- Question 18: **A. X (no article)**
- Question 19: **D. danger**

**SCHOOL ANNOUNCEMENT**
- Question 20: **A. learning**
- Question 21: **B. encourage**
- Question 22: **C. who**

So, the final answers are:
- 17. D
- 18. A
- 19. D
- 20. A
- 21. B
- 22. C