Final answer:
The auditors should issue a Disclaimer of opinion in this case option a.
Step-by-step explanation:
The auditors should issue a Disclaimer of opinion in this case. A Disclaimer of opinion is issued when the auditors are unable to form an opinion due to a significant scope limitation or lack of sufficient evidence. In this situation, the auditors are unable to determine the misstatement involved in the client's accounting for deferred income taxes, so they cannot form an opinion on the financial statements as a whole.