Step 1: Concept
Alignment and registration are critical adjustments for any machine using a reciprocating cutter bar.
Step 2: Meaning
Registration refers to the knife section being exactly centered in the guard at the end of each stroke. Alignment ensures the cutter bar is at the correct angle to the direction of travel.
Step 3: Analysis
Reapers (and mowers) use reciprocating knives to cut the crop stalks. If registration is off, the machine will tear the crop rather than cut it cleanly.
Step 4: Conclusion
Therefore, these terms are specifically associated with the reaper.
Final Answer: (D)