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 paths are equal to each other assuming the field induction vector \[\vec{B}\] 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. \[2\]