The human GM-CSF gene and the mouse GM-CSF gene vary by more than 60% in their DNA sequence. However, when scientists place the human gene into mice, it functions properly. What best explains why this happens?

The difference between gene sequences does not change the structure of the proteins.
The resulting proteins made by the human gene are similar to the proteins made by the mouse gene.
The mouse DNA is a mutated form of the human GM-CSF gene.
Mice can make human protein without the use of the human GM-CSF gene.