Step 1: Concept
Hydraulic systems in tractors require high-pressure, positive displacement pumps to operate lifts and steering.
Step 2: Meaning
Positive displacement pumps deliver a fixed amount of fluid per revolution, which is necessary for generating significant force.
Step 3: Analysis
The gear pump is the most common choice for tractor hydraulics because it is simple, durable, and handles high pressures efficiently.
Step 4: Conclusion The gear pump is the standard component for developing hydraulic pressure in tractors.
Final Answer: (D)