Which of the following statements about acetal formation from an aldehyde and an alcohol are correct?

1. AAcid is needed for hemiacetal to acetal conversion because the OH must be converted into a better leaving group.
2. B$\mathrm{NaOCH}{}_3$ in $\mathrm{CH}{}_3\mathrm{OH}$ converts an aldehyde fully into its dimethyl acetal.
3. CThe oxocarbenium ion intermediate is stabilised by donation of an oxygen lone pair.
4. DAcyclic simple hemiacetals are generally in equilibrium with the carbonyl compound and are not isolated.