Why Would an Auditor Issue a Disclaimer of Opinion with Regards

Why would an auditor issue a disclaimer of opinion with regards to an audit of financial statements? What does this type of opinion mean?.
a)________ Internal controls are used to provide reasonable assurance that the objectives of an enterprise will be accomplished.b)________ Internal controls can be divided into accounting controls and administrative controls.c)________ The mechanics of internal control systems do not vary from company to company.d)________ Accounting controls are concerned with the evaluation of performance and the assessment of the degree of compliance with company policies and public laws.e)________ Administrative controls are composed of policies and procedures that are designed to safeguard the assets and to assure that accounting records contain reliable information.