Let's analyze the statements:
Statement A: The ratio of supervisors to clerks is 4:5, but it doesn’t provide the total number of employees.
Statement B: The total monthly salary of supervisors is 28% more than that of clerks, but it doesn't give the total number of employees.
Statement C: 20% of clerks' monthly salary is Rs. 25,000, giving salary info but no details on supervisors or total employees.
Combinations:
1. A and B together: Provides the ratio and salary relationship but not the total number of employees.
2. A and C together: Gives the ratio and clerks' salary but still not enough for the total number of employees.
3. C alone: Provides salary info for clerks but not for supervisors or total employees.
4. All statements combined: Still insufficient to determine the total number of employees.
So, the correct option is (D): The question can't be answered even after using all the information.