$---\left(1\right)--$ is a/an $-\left(2\right)-$ recessive trait that can be transmitted from parents to the offspring when both the parents are $-\left(3\right)---$.

Read the following statements:
(a) Genes are the units of inheritance.
(b) Gene contains the information that is required to express a particular trait in an organism.
(c) Gene which codes for a pair of contrasting traits is are known as alleles.
(d) Mendel called gene as 'factors'.

Pick up the incorrect statement: