Answer (B).
The attributes of a candidate key are called the prime attributes. Suppose $ABC$ is one candidate key of a Relation $R(ABCDEFGH).$ Then the attributes $A, B$ and $C$ all are prime attributes. Similarly if $ABD$ is also another candidate key in the same relation $R,$ then $D$ is also a prime attribute. And conversely, an attribute that does not occur in ANY candidate key is called a non-prime attribute.