Consider each of the following independent situations which have come to your attention:

a) Upon review of the recent history of their specialized mining equipment Minco Limited changed the service lives for depreciation purposes on this equipment from five years to three years. This change resulted in a material amount of additional depreciation.

b) The management of Surf Limited's has refused to disclose a few, director related transactions on the grounds of commercial confidentiality. The financial controller reminds you that no other errors have been found in the financial report and states that the transactions are immaterial and therefore irrelevant to the users of the financial report.

Required: For given circumstances, identify the type of audit opinion that should be issued and justify your response