Choice "C" is correct. An analysis of the repairs and maintenance account would best aid the auditor in verifying that all fixed assets have been capitalized. This account is generally analyzed to test for completeness of asset additions (i.e., the auditor is looking for items recorded as repairs or maintenance that would more properly have been capitalized as betterment of an asset).
Choice "b" is incorrect. An analysis of cash would not identify fixed assets that were not properly capitalized, since cash would be paid for the purchase regardless of whether the item were expensed or capitalized.
Choice "a" is incorrect. An analysis of depreciation expense would not identify fixed assets that were not properly capitalized, since no depreciation would be included for items not already classified as assets.
Choice "d" is incorrect. An analysis of property tax expense would not identify fixed assets that were not properly capitalized, since no property tax would be included for items not already classified as assets.