You are correct, the answer A) Stop loading is the correct first action to take. The reasoning is that when an oil spill is observed, the immediate priority is to stop the source of the spill, which in this case is the ongoing loading of the bulk oil. Stopping the loading will prevent further oil from being released into the water. The other options, while important, are secondary actions that should be taken after the loading has been stopped. Notifying the Coast Guard and terminal superintendent are necessary to report the spill, while searching the vessel for leaks may help identify the source, but these steps should not take priority over stopping the active spill.