The correct option is C Alpha particle
Alpha particles can be shielded by a piece of paper.
To discriminate the types of radiation, all you need to do is understand the
characteristics of your particular probe, and have a few pieces of
"absorber" material on hand.
If the radiation is stopped by a single piece of typing paper, it is
undoubtedly Alpha particles. If it takes a piece of tin foil or a very thin
aluminum sheet to stop most of it, you are probably looking a Betas. Of
course the tin foil also stops all Alphas too.
Gamma rays will easily pass through steel, aluminum and it takes 1" of lead
to stop even 1/2 of it.