A proton and a deuteron are projected with same speeds normal to a uniform magnetic field. Which of the following statements is `//` are true
`a)` The ratio of their respective time periods is `1:2`
`b)` The ratio of their respective angular momenta about the centres of their circular path is `1:4`
`c)` The ratio of their respective radii of their circular is `1:2`
A. only `a`
B. only`c`
C. only `a,b`
D. All are true
