In Mendelian cross, codominance and incomplete dominance the heterozygous will always have a unique phenotype. As they don't differ in this matter, B is incorrect.
There is a heterozygous phenotype and it is different than a homozygous recessive or a homozygous dominant, and it applies to Mendelian cross, to codominance and to incomplete dominance as well. Therefore, C and D are also incorrect.
The Mendelian laws of inheritance does not identify codominance or incomplete dominance, but it can lead to their identification as they do not differ in its function. Therefore, the correct answer is A. There is no difference.