Step 1: Understanding the Concept:
Felt manufacturing involves specific processes.
Each process has a distinct function.
Step 2: Key Formula or Approach:
No specific formula.
Need to know felt manufacturing.
Step 3: Detailed Explanation:
Milling is the process in felt manufacturing.
It combines heat, moisture, and mechanical energy.
This causes fibers to interlock and form felt.
Sorting is the initial separation.
Hardening and drying are subsequent steps.
Thus, milling is the correct answer.
Step 4: Final Answer:
The combination of heat, moisture, and mechanical energy is milling.
Hence, the correct option is (B).