If you compare carefully house prices in the two areas, it is quietly amazing how different they are.

Explanation

Analysis: The word "quietly" is incorrectly used in this context. The correct word should be "quite," which means "to a certain extent" or "very." "Quietly" means "in a quiet manner," which doesn't fit the context.Conclusion: This option contains the error.Quietly: This option is the correct one to mark, as "quietly" is incorrectly used. The correct word should be "quite."Explanation:"Compare carefully" is acceptable but could be improved stylistically to "carefully compare.""Quietly" is incorrect; "quite" is the correct word."How" is correctly used to introduce the extent of the difference."They are" is correctly used to describe the difference.So, the correct answer is B) Quietly.