Rays easily penetrate through the human body and require lead or several inches of concrete to prevent penetration.

a. beta
b. alpha
c. neutron
d. gamma

Gamma rays can easily penetrate through human body and require lead or several inches of concrete to prevent penetration.

Explanation:

Radioactive rays can be alpha, beta and gamma rays. Each kind of rays has their own penetrating properties. Alpha rays have the least ability to penetrate and thus they can be stopped by a paper itself. While beta have higher penetration power compared to Alpha rays and they can be stopped by aluminium shield. While the most penetrating properties are of gamma rays. The gamma rays are the one which has the capability to penetrate human body and tissues and affect them seriously. So gamma rays can be stopped by using lead or several inches of concrete as shield.