Answer:
The right answer to this question is B. Norm of reaction for height.
Explanation:
Norm of reaction is a type of study that focus on a single genotype, and how it'll influence the phenotype of the species in different environments. In this case, we're studying Achillea Millefolium, that according to the question, depends on one specific genotype to be or not to be tall. Through this information given by the question, we can be sure that this is a norm of reaction, because after that, to check if the plant is tall of not, we test it on different environments, confirming the norm of reaction again.