When I choose “Peers” option, I can see many IP, d/l and u/l rate. Also, I can see many peers have been 100%. But , why can I d/l from these peers? Can I select these peers to d/l in BitComet? I use 0.70 version 
No, you can’t. Bittorrent manages its own connections much better than you can, so it chooses the best, most reliable connections to use. The network dynamic is constantly changing, so it’s going to be more aware of, and do a better job of managing it than you can.
Thanks for your reply. But it is pity for can’t change the better connection
I agree with sfriend on this. I posted a question about download upload logic a week or so ago, but nobody replied.
The client program may have a much better overall understanding, but sometimes it would be nice to have an override. And after all it works both ways, not just in greedy downloading. Manys the time I have been seeding a file and there is someone sitting there on 99% and he won’t download from me. I just feel like saying sorry guy if only I could help, but I can’t