You have a mutant plant, mut-x and, compared to wild-type plants, it fails to respond to blue light. Definitive proof that the loss of the X protein is responsible for the phenotype would be: a. to show that mut-x plants respond to all other wavelengths of light normally b. to prove that the wild-type MUT-X protein can absorb blue light c. to take wild-type plants, add the (mutated) mut-x gene to them, and test their response to blue light d. to transform mut-x plants with wild-type (normal) X gene and show they behave normally under blue light.