The correct answer is B) DC motors offer a more effective means of controlling speed than AC motors. The key advantage of DC motors over AC motors is the ability to precisely control the speed of DC motors through electronic speed control. DC motors can easily be integrated with electronic speed controllers, which allow for fine-tuning of the motor speed. This makes DC motors more suitable for applications that require variable speed control, such as in machinery, elevators, and electric vehicles. In contrast, while AC motors can also have variable speed control, the methods are generally more complex and less precise compared to DC motor speed control. The other answer choices are not as accurate. A) is incorrect as both AC and DC motors can be started across the line. C) is incorrect as AC motors can actually require less maintenance than DC motors in some applications. D) is incorrect as the relative cost of AC vs DC motors can vary depending on the specific application and requirements.