Sure! Let's analyze the passage and fill in the blanks with the most appropriate answers:

1. **21. A. valley | B. forest | C. mountain | D. desert**
The correct answer is **C. mountain**. The passage states that "Mount Everest is located in the Himalayan mountain range," and since we are referring to Mount Everest specifically, it should be classified as the world's highest mountain.

2. **22. A. higher | B. longer | C. wider | D. deeper**
The correct answer is **A. higher**. The context indicates that we are comparing the height of Mount Everest to Empire State Buildings, so "higher" is the appropriate term to describe a greater vertical distance.

3. **23. A. beginning | B. increasing | C. getting | D. following**
The correct answer is **B. increasing**. The sentence mentions how Mount Everest "is increasing in height by a 1/3 of an inch every year." The word "increasing" best conveys the idea of rising in height over time.

4. **24. A. travel | B. come | C. arrive | D. reach**
The correct answer is **D. reach**. You "reach the summit" rather than just "travel," "come," or "arrive" at it. The term highlights successfully attaining the highest point.

5. **25. A. youngest | B. oldest | C. strongest | D. boldest**
The correct answer is **B. oldest**. The context specifies the age of the person who climbed Mount Everest, so "oldest" is appropriate to describe the person who made the climb at the highest age.

Here is the completed passage with the correct answers filled in:

- 21: C. mountain
- 22: A. higher
- 23: B. increasing
- 24: D. reach
- 25: B. oldest

If you need further clarifications or explanations about any particular step, feel free to ask!