The correct answer is A) chemical agents. The use of chemical agents to clean up oil spills in U.S. waters is regulated by the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). According to the NCP, the Federal On-Scene Coordinator must approve the use of chemical agents, such as dispersants, before they can be applied. This is to ensure that the use of such chemicals is appropriate and does not cause more environmental harm than the oil spill itself. The other options, B) skimmers, C) straw, and D) sawdust, are mechanical or natural methods of oil spill response that do not require the same level of approval from the Federal On-Scene Coordinator.