Here are the correct answers for each question:

1. **If she** **_visits_** **the new community center tomorrow, she** **_will learn_** **more about the upcoming events.**

2. **According to Minh, participating in a team sport is** **_more challenging_** **than playing an individual sport because it requires more cooperation and communication.**

3. **By the time the concert started, they** **_had been standing_** **for over two hours in line, waiting for their tickets to be checked.**

4. **To stay healthy, you should eat** **_less_** **junk food and choose healthier options instead.** (The correct option was not provided, but "less" would be appropriate. If limited to your options, "a lot of" could fit a context where you want to express avoiding excessive junk food.)

Note: In question 4, it seems like there may have been a typographical or contextual error with the available choices, as the correct concept should be "less" for reducing junk food rather than any of the provided choices.