Sorry first time using forum and I don't know how to post pictures. But basically the other night in class we had an issue sizing bonding jumpers. I had the understanding that you added up your largest ungrounded conductor size in each pipe together, then look at table 250.102 and size the bonding jumper based off that. Or size off the amperage of the main and go to table 310.16, and get the size there. That being said I still don't understand why the answer to 3 is D and not E. And why the answer to 6 is C and not D. Thank you in advance.