A student puts forward three ways of demagnetising a piece of steel. $1$ holding it in an east-west direction and striking it hard $2$ holding it in an east-west direction and heating it until it glows red hot $3$ drawing it out slowly from a coil carrying alternating current Which of these methods will demagnetise the piece of steel?
- A1 only
- B2 only
- C3 only
- D1, 2 and 3