ACC - What AU standard contains information about derivatives

1. What AU standard contains information about derivatives and securities that should be included in the management representation letter?

2. What AU-C standard provides guidance to the auditor regarding the use of a service provider (for example, a service provider that helps a company to process its payroll for employee)?

3. What AS standard (PCAOB) provides guidance about what an auditor should do regarding the internal control of a service provider (see question above) in the internal control of a company?

4. What AU-C standard provides information about what is usually contained in the standard legal letter requested from attorneys regarding the outstanding litigation or claims of a company?