The correct answer is: A. Pumping sets
DC motors are widely used in pumping sets because they are simple to control and can be operated at a wide range of speeds. They are also efficient and reliable, making them a good choice for applications where continuous operation is required.
Air compressors are also a common application for DC motors, but they are not as widely used as pumping sets. This is because air compressors require a higher starting torque than pumping sets, and DC motors are not as well-suited for this application.
Electric traction is another application for DC motors, but it is not as common as pumping sets or air compressors. This is because electric traction requires a high power-to-weight ratio, and DC motors are not as efficient as other types of motors, such as AC motors.
Machine shops are a common application for AC motors, but they are not as widely used for DC motors. This is because AC motors are more efficient than DC motors, and they are also easier to control.
In conclusion, DC motors are widely used in pumping sets because they are simple to control and can be operated at a wide range of speeds. They are also efficient and reliable, making them a good choice for applications where continuous operation is required.