The correct answer is option 'B': Carbon steel screw and phosphor bronze nut.

Explanation:
- Power screws are used in various mechanical systems to convert rotary motion into linear motion. They are commonly used in applications such as jacks, presses, and clamps.
- The combination of materials used for the screw and the nut is important to ensure smooth operation, long life, and efficient power transmission.
- In this case, a carbon steel screw and a phosphor bronze nut are the ideal combination of materials for power screws. Let's understand why:

Carbon steel screw:
- Carbon steel is a strong and durable material that can handle high loads and resist wear and tear.
- It has good mechanical properties such as high tensile strength, hardness, and toughness, which are important for power transmission.
- Carbon steel screws are commonly used in power screws because they can withstand heavy loads and provide reliable operation.

Phosphor bronze nut:
- Phosphor bronze is a type of bronze alloy that contains a small amount of phosphorus.
- It has excellent mechanical properties such as high strength, good wear resistance, and low coefficient of friction.
- Phosphor bronze nuts are preferred for power screws because they offer smooth and reliable movement, low friction, and resistance to wear.
- They also have good corrosion resistance, which is beneficial in applications where the screw and nut may be exposed to moisture or other corrosive environments.

Advantages of the combination:
- The combination of a carbon steel screw and a phosphor bronze nut provides a good balance of strength, durability, and smooth operation.
- Carbon steel screw can handle high loads and resist wear, while the phosphor bronze nut ensures low friction and reliable movement.
- This combination is suitable for a wide range of applications and provides efficient power transmission.

In conclusion, the ideal combination of materials for power screws is a carbon steel screw and a phosphor bronze nut. This combination offers strength, durability, low friction, and reliable operation, making it suitable for various mechanical systems.