Step 1: Concept
The lathe machine consists of several primary units that perform specific functions in metal turning.
Step 2: Meaning
The unit located at the left end of the lathe provides the power and rotation to the workpiece.
Step 3: Analysis
The Headstock contains the main spindle, which holds the chuck or centers, and the gear mechanism or step pulleys used to vary the rotational speed. The Tailstock supports the other end of the work, and the carriage holds the cutting tool.
Step 4: Conclusion
Therefore, the Head Stock is the correct unit.
Final Answer: (B)