Let's analyze the questions based on the context provided in the text:

### Question 17
You need to fill in the blank with a sentence that logically completes the given text about a picnic trip.

1. **A** - This sentence follows logically, as it reflects disappointment after an unfortunate event.
2. **B** - This doesn't strongly conclude the story; it's more of a side comment.
3. **C** - This seems more to add extra detail rather than provide a conclusion.
4. **D** - This can fit, but doesn't capture the essence of a conclusion after feeling disappointed.

**Correct Answer**: **A** - It best encapsulates the disappointment and conclusion of the picnic narrative.

### Question 18
You need to choose the correct answer based on the context related to cities.

1. **20**: Here, you're looking for a phrase that describes the condition of urban life.
- **A** - “highly living cost” is incorrect.
- **B** - “high cost of living” is grammatically correct and contextually appropriate.
- **C** - “costly high living” is awkward.
- **D** - “living costs high” is grammatically awkward.

**Correct Answer**: **B** - It correctly depicts the concept.

2. **21**: You need a term that makes sense in the context of traffic issues.
- **A** - “Rent” doesn’t fit the context.
- **B** - “the cars” is specific but not general.
- **C** - “cars” works, but doesn't connect well.
- **D** - “There are cars” is awkward in this context.

**Correct Answer**: **B** - “the cars” fits contextually about the problem discussed.

3. **22**: This asks how cities address the mentioned traffic issues.
- Options need to convey a clear purpose.
- **A** and **B** don't appropriately fit the context.
- **C** - “Tackling” and **D** - “To tackle” can work, but **D** as an infinitive sounds better.

**Correct Answer**: **D** - “To tackle” provides a clearer forward-looking solution.

### Final Selections:
- **Question 17**: A
- **Question 18(20)**: B
- **Question 18(21)**: B
- **Question 18(22)**: D

### Explanation:
These responses were selected based on their grammatical correctness and the coherence with the surrounding text, ensuring a logical flow that aligns with the context of urban living challenges.