Answer:
Option C= several cm of lead.
Step-by-step explanation:
we know there are three types of radiations emit by the atoms to attain the stability. These three radiations are alpha, beta and gamma. Gamma radiations are high energy radiations. These radiations are travel at the speed of light. Gamma radiations can penetrate into the many materials. These radiations are also used to treat the cancer.
These radiations can not be stopped by the single sheet of paper or the water. Lead is used for the protection against gamma radiations because of its high molecular density. The lead apron are used by the person when treated with gamma radiations. Lead shields are also used in the wall, windows and doors of the room where gamma radiations are treated, in-order to protect the surroundings. While the sheet of aluminium is used to block the beta radiations.