Which of the following is/are performed in an audit of internal control over financial reporting?

Which of the following is/are performed in an audit of internal control over financial reporting?

Which of the following is/are performed in an audit of internal control over financial reporting?

    a.    Procedures to obtain an understanding of internal control
    b.    Tests of controls
    c.    Both a and b
    d.    Either a or b, but not both