Choice "C" is correct. Client-imposed restrictions of scope such as those caused by inadequate records would cause the auditor to choose between issuing a disclaimer of opinion and a qualified opinion.
Choice "a" is incorrect. An unmodified opinion would only be justified if the transactions in question were not material, but in such situations, no emphasis-of-matter paragraph would be required.
Choices "b" and "d" are incorrect. An adverse opinion pertains to GAAP and would not be used for reporting restrictions of scope.
