Indicate which of the following statements is TRUE with respect to internal controls. (check all that apply) Select one or more: a. Fraud committed by top-level employees is more difficult to detect because those employees more often have the ability to override internal control procedures. b. The components of internal control are built on the foundation of the ethical tone set by top management. c. Collusion refers to the act of a single individual circumventing internal control procedures. d. Historically, customer tips have been the most common means of detecting employee fraud.