The velocity ratio of a differential wheel and axle with 'D' as the diameter of effort wheel and d1 and d2 as the diameters of larger and smaller axles respectively, is

• A. D/(d‚Äö√á√Ö + d‚Äö√á√á)
• B. D/(d‚Äö√á√Ö - d‚Äö√á√á)
• C. 2D/(d‚Äö√á√Ö + d‚Äö√á√á)
• D. 2D/(d‚Äö√á√Ö - d‚Äö√á√á)