Which of the Following Is True About ARCH and GARCH

Multiple Choice

Which of the following is true about ARCH and GARCH models?
(I) They are used for modelling and forecasting volatility
(II) They are non-linear models
(III) They can both be estimated using OLS
(IV) Series estimated using these models must have a unit root process

A) I only
B) I and II only
C) I, II and III only
D) I, II, III and IV