For a four-stroke engine, two revolutions complete one cycle and hence, If speed is 2000 rpm then the number of complete cycles per minute is 1000.

To understand how many power strokes are completed by a four-stroke engine with a single cylinder rotating at 2000 RPM, we need to first understand the basics of a four-stroke engine and its operating cycle.

A four-stroke engine completes four distinct strokes in its operating cycle: intake, compression, power, and exhaust. Let's break down the operating cycle and calculate the number of power strokes completed in one minute.

1. Intake Stroke:
During the intake stroke, the piston moves downward, allowing the intake valve to open and the fuel-air mixture to enter the combustion chamber. This stroke does not produce any power.

2. Compression Stroke:
After the intake stroke, the piston moves upward, compressing the fuel-air mixture. This stroke also does not produce any power.

3. Power Stroke:
In the power stroke, the compressed fuel-air mixture is ignited by a spark plug, causing a rapid expansion of gases. This expansion pushes the piston downward, generating power.

4. Exhaust Stroke:
Finally, the piston moves upward again, pushing the exhaust gases out through the open exhaust valve. This stroke does not produce any power.

Now, let's calculate the number of power strokes completed in one minute:

- A four-stroke engine requires two complete rotations (720 degrees) of the crankshaft to complete one operating cycle.
- Since the engine is rotating at 2000 RPM (revolutions per minute), the crankshaft completes 2000 revolutions in one minute.
- Each revolution consists of two complete rotations, so the number of operating cycles completed in one minute is 2000/2 = 1000.

Therefore, the engine completes 1000 power strokes in one minute.

Hence, the correct answer is option 'c) 1000'.

C