The ratio of de-Broglie wavelength of a a-particle to that of a proton being subjected to the same magnetic field so that the radii of their path are equal to each other assuming the field induction vector \[\overrightarrow{B}\] is perpendicular to the velocity vectors of the a-particle and the proton is

• A.            1    
• B.            \[\frac{1}{4}\]
• C.            \[\frac{1}{2}\]                      
• D.            2