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Question 2: the donut looks like made from Polyethylene. Please see the Nodes blew.
There is the final one, looks like a one-week-old donut. lol
There is the node.
Thanks for your time~
Answers found by myself.
1. there are duplicated vertices because I hit E and did not do anything then hit E again.
2. Aged donut because I forgot to give subsurface to the donut.
I hope this can help anyone who has the same problems. It is just so much to learn.
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