Detailed Explanation:

Rationale for Correct Answer: A kickback scheme occurs when vendors make payments to employees of a purchasing organization in exchange for steering business their way. Here, Bob steered contracts to Oak Company and received a percentage of profits, a textbook kickback arrangement.

Analysis of Incorrect Options:

B. Illegal gratuity scheme – Involves rewards after a decision, without a prior agreement. Here, the agreement was prearranged.

C. Diversion scheme – Refers to diversion of assets, not procurement favoritism.

D. Economic extortion scheme – Involves coercion of the vendor; this was voluntary bribery.

Key Concept: Bribery and kickbacks as forms of corruption.