Hello! Your answer is A, blue is dominant to white.
A dominant gene means that it is always expressed if present, no matter what other genes there are. For example, if there is a dominant blue gene, and a recessive red gene, blue will be expressed.
In this case, we see that all three children are blue. This shows that blue is most likely dominant, and white is recessive.
Let's approach the other case, that white is dominant to blue. If white is dominant, then the blue smurf must have two blue recessive traits, and the white smurf would either have two white dominant traits, or one white and one blue trait. The only possible way the children can have a blue color is if the white smurf is heterozygous (meaning it has two different genes, in this case one blue and one white), and passes down the recessive gene three times. As you can see, this is very unlikely.
If white and blue are codominant, then the children would have a mixture of the two genes. (Most likely). This is not the case.
Therefore, your answer is A.
Hope this helps!
