Here are the corrections for each sentence:

27. **C. go out** - should be corrected to "go". The correct sentence is: "We don’t know if to wait for the others to go and enjoy street food in Ho Chi Minh City."

28. **A. about** - should be corrected to "in". The correct sentence is: "She looked in the school’s neighbourhood because she didn’t know where to buy a pencil case."

29. **A. the** - should be corrected to "best". The correct sentence is: "They asked a lot of questions, checked their figures, and came up with the best solution."

30. **B. who** - should be corrected to "to". The correct sentence is: "Do you know how to find information on local community initiatives and projects?"

So, the corrections are:
27. C
28. A
29. A
30. B