Choice "D" is correct. The auditor reviews repair and maintenance expense accounts 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 "a" is incorrect. Analyzing the repairs and maintenance account does not provide evidence about obsolete assets. The auditor might review asset records for old assets, or observe assets that are not being used, in an effort to determine whether obsolete plant and equipment assets were written off before year-end.
Choice "b" is incorrect. Analyzing the repairs and maintenance account does not provide evidence about the existence of assets. The auditor might select recorded plant and equipment assets, and then physically locate and observe them, in order to verify existence.
Choice "c" is incorrect. Analyzing the repairs and maintenance account does not provide evidence about assets that cannot be repaired. The auditor might review asset records for old assets, or observe assets that are not being used, in an effort to determine whether assets that cannot be repaired have been properly written off.