A Pair- Rule Gene in Drosophila Called Runt Controls Nervous

A pair- rule gene in Drosophila called runt controls nervous system formation. In the mouse, runt controls blood cell formation and genital structures. In humans, the analog of runt, when mutated, causes children to lack collar bones, and the opening at the top of the skull fails to close. What kind of experiment could tell you whether these genes are conserved in function?

A) sequencing the proteins encoded for by each of the species' runt genes
B) an in vivo experiment that replaces the coding sequence of Drosophila runt gene with the coding sequence from the homologous mouse runt gene to see if the mouse gene allows the nervous system to develop.
C) use of immunological methods to identify the target cells of the species' runt transcription factors
D) an in vitro experiment that identifies the DNA binding sites of the Drosophila runt gene.
E) sequencing of the runt genes from each of the three species