Which of the Following Are Allowable Methods of Dealing with a Discount

Which of the following are allowable methods of dealing with a discount on issue of debentures?
1) Amortise the discount by straight line over the life of the debenture as an annual period expense to profit and loss
2) Amortise the discount by reducing balance over the life of the debenture as an annual period expense to profit and loss
3) Recognise the whole discount immediately as a period expense
4) Amortise the discount by adjusting (increasing) interest expense over the life of the debenture

A) 1, 2 and 3
B) 1, 2 and 4
C) 1, 2, 3 and 4
D) 4 only