Final answer:
The speed control lever for a model 421437-0117 engine's reference number cannot be accurately determined from the given options without the specific engine's manual or parts diagram.
Step-by-step explanation:
The speed control lever for a model 421437-0117 engine is listed with a reference number to identify the specific part in the engine's diagram or parts list. A thorough search through the suggested reference numbers provided does not match the specific part number for the speed control lever. Without the correct diagram or additional context, it is not possible to accurately determine the reference number for the speed control lever from the options provided (A. 201, B. 223, C. 621, D. None of the above). It would be advisable to consult the specific engine's manual or parts diagram to find the correct reference number for the speed control lever.