9.True. Someone with type AB blood has no antibodies against type O, since type O does not have antigens on the RBCs, so there is no negative immune response.
You are right, but I think you need to understand the difference between co-dominance and incomplete dominance.
It's easier to use a plant for incomplete dominance. Say that red flowers (R) and white flowers (W) are incompletely dominant to each other. If a plant with red flowers (RR) is matched with a plant with white flowers (WW). The flowers will be RW, a mix of red and white, so they will be pink. That's incomplete dominance.
With blood type, A and B are co-dominant, so if a person inherits one type A gene and one type B gene he will have both traits clearly expressed (type AB blood) and not mixed, as with the pink flowers, which are neither red or white but a mixture of both.
I hope this helped!