27. a. quieter - We use comparatives ("quieter") to compare two places. "Elderly" refers to old people.

28. c. fastest - We use superlatives ("fastest") to compare three or more things. "More fast" is grammatically incorrect.

29. b. fewer - "Fewer" is used for countable nouns (books). "Least" is a superlative used for all types of nouns.

30. c. richest - "Richest" is the superlative form of "rich" to compare wealth among multiple people.

31. b. thinner - We use comparatives ("thinner") to compare two people or things. "Elderly" refers to old people.

32. d. the best - "The best" is the superlative form of "good" used to identify the absolute best.

33. c. much better - "Much better" is a comparative phrase used to show a significant improvement.

34. c. the tallest - "The tallest" is the superlative form of "tall" used to identify the person with the greatest height in the class.

35. A. smartest - "Smartest" is the superlative form of "smart" used to identify the most intelligent student based on grades.

36. C. the most beautiful - "The most beautiful" is the superlative form used to show this building is absolutely more beautiful than any other mentioned.

37. C. funniest - "Funniest" is the superlative form of "funny" used to identify Susan as the most humorous among the three girls.

38. B. largest - "Largest" is the superlative form of "large" used for size comparisons. "Most largest" is grammatically incorrect.

39. B. more careful - "More careful" is the comparative form used to show Dorothy is more cautious with money compared to you.

40. D. loveliest - "Loveliest" is the superlative form of "lovely" used to express your opinion that Hanoi is the most charming city globally.