High-pressure drip irrigation system works at operating pressure of -

Correct option is D

The correct answer is (d) 30 psi or more. 
Explanation:
High-pressure drip irrigation systems typically operate at pressures above 30 psi. This is distinct from low-pressure systems which operate at pressures below 20 psi. Some sources define high-pressure systems as operating between 30-50 psi, while others use a higher threshold of 60 psi or more for systems like those used in large-scale agriculture or with wastewater applications. 
Why other options are incorrect:
· (a) Less than 10 psi:
This pressure range is typical for low-pressure drip irrigation systems. High-pressure systems require higher pressures to overcome friction losses in longer runs and deliver consistent water flow rates. 
· (b) Less than 20 psi:
While some high-pressure systems might operate at the lower end of this range, most fall above 20 psi. The majority of drip irrigation systems, both low and high-pressure, operate within a range of 10-50 psi. 
· (c) Less than 30 psi:
This option is partially correct. While some high-pressure systems may operate at the lower end of this range (20-30 psi), true high-pressure systems consistently exceed 30 psi. Many pressure reducers are designed to lower incoming water pressure to this 30 psi range for use in drip irrigation systems. However, the actual operating pressure of the system itself is typically higher.