Which of the following provides the strongest evidence for the conservation of tool-kit genes? a. Bicoid moved from one fly embryo into the posterior of another fly embryo causes the formation of two head regions. b. Mutation of an unrelated gene in another species of fly has a similar effect to mutation of bicoid in Drosophila. c. A mouse Hox gene can be used to take over the function of a mutated Drosophila Hox gene. d. Sheep can be cloned by fusing a differentiated adult cell with an enucleated egg.