Question

which of the following resulted from codominance? 1)a person with AB blood type 2)a flower with pink petals 3)a rabbit with white fur 4)a mouse with brown fur

Answer 1

1) As blood groups A and B are equally dominant so the individual will express both characteristics in the phenotype. 
Notice how in all the 3 other examples the organism is only expensive 1 version (allele) of each gene. For example the mouse with brown fur may have 2 brown fur alleles (and so would have to express this characteristic even if it was recessive) but it could have 1 allele which is less dominant than the brown, in which case brown would be expressed. In this case the alleles were not co-dominant.