You have a circular plasmid containing 9kb of DNA, and you wish to map its EcoR1 and BamHI sites. When you digest the plasmid with EcoRI and run the resulting DNA on a gel, you observe a single band at 9kb. You get the same result when you digest the DNA with BamHI. When you digest with a mixture of both enzymes, you observe two bands, one 6kb and the other 3kb in size. Explain these results. Draw both a picture of what the gel would look like with all three digest and a map of the restriction sites.