Describe a filter-binding assay to measure binding between a DNA and a protein.

a) The DNA is labeled with a radioactive isotope and then mixed with the protein. The mixture is passed through a filter, and the amount of radioactivity retained on the filter indicates the extent of binding.
b) The DNA and protein are mixed together and then heated to denature the complex. The denatured complex is then passed through a filter, and the amount of DNA retained on the filter indicates the extent of binding.
c) The DNA is mixed with a fluorescent dye and then incubated with the protein. The mixture is passed through a filter, and the fluorescence retained on the filter indicates the extent of binding.
d) The DNA is labeled with a fluorescent dye and then mixed with the protein. The mixture is passed through a gel electrophoresis system, and the fluorescence detected on the gel indicates the extent of binding.