Just after watching Harry Potter, I have three questions to ask.

A, the teacher of divination class is Trelawney, and the teacher of Muggle Studies class is dead (name forgotten). You can read the original text.

B, when the trio was arrested at Malfoy Manor, Hermione deformed Harry's face. Harry said he was Dali, and then Bellatrix asked Draco to identify him as Harry. Draco recognizes him, but if he says Harry, it may be dangerous (Bella will inform Lord, and Lord will come back to kill Harry).

C, that ring is the resurrection stone. Albus dumbledore accidentally killed his sister arianna, and he always felt guilty about it. So he couldn't stand the temptation of the Resurrection Stone (when Harry went to the Pig's Head Bar to find Aberforth, the girl in the portrait on the wall was arianna ~), and the Dark Lord put a curse on the ring. In fact, whoever wears that ring will die, but Dumbledore is stronger, so he didn't die at once.

I hope I can help you ~