Here are the answers to the questions based on the passage provided:

**Question 28:** How can teenagers keep fit?
- **Answer:** A. Balance their lifestyle

**Question 29:** What is the benefit of a balanced diet?
- **Answer:** B. Functioning better brain

**Question 30:** What does "These" refer to?
- **Answer:** D. Five groups of foods

**Question 31:** Which has the closest meaning to "engage"?
- **Answer:** B. participate

**Question 32:** What is the best title for this passage?
- **Answer:** (Not provided in the options, but a suitable title could be "Living a Balanced Lifestyle.")