Progeny with blood group $‘O’$ can not be obtained in cross

Explain the following terms with example

$(a)$ Co-dominance

$(b)$ Incomplete dominance

For a child having blood group $B$, if father has blood group $A$, what may be the blood group of the mother

In short horned cattle, genes for red $(R)$ and white $( r )$ coat colour occur. Cross between red $(RR)$ and white $(rr)$ produced $(Rr)$ roan. This is an example of

The father has blood group $AB$ and mother $‘O'$. The child is supposed to have which of the following bloodgroups

In the $ABO$ system, of blood group which of the following is example of co-dominance ?