The correct answer is aluminium.
Beta radiation consists of electrons that are ejected by the nucleus. Beta particles have the charge of an electrons and the mass of an electron. Beta particles are quite small , giving them the ability to travel through materials a bit longer before collisions with other particles makes them stop hence they can not be stopped by skin, a piece of paper and thin fabric. Their size accounts for why they have more penetration abilities than alpha particles which are large and can be stopped by a thin piece of paper. However, it is known that a few millimeters of aluminium sheet is able to stop beta particles.
The correct answer is aluminium.