Which best describes a recessive allele?

a) always inherited from a parent when a dominant allele is inherited from the other parent
b) never inherited from a parent when a dominant allele is inherited from the other parent
c) only determines phenotype when a dominant allele for the same trait is present
d) does not determine phenotype when a dominant allele for the same trait is present
Please help!!! I think the answer is a but i'm not sure.