What was the claimed maximum output of the Mercedes-Benz M21 engine?

A. 40 PS (29 kW; 39 hp) at 3,200 rpm
B. 50 PS (37 kW; 49 hp) at 3,500 rpm
C. 30 PS (22 kW; 30 hp) at 2,800 rpm
D. 60 PS (44 kW; 59 hp) at 3,800 rpm
Answer: 