Which of the following statements about the free radical polymerisation of ethene to low density polyethene is/are correct? (One or more options may be correct.)

1. AIt is initiated by a trace of dioxygen or a peroxide at high pressure.
2. BA catalyst of $\mathrm{TiCl}{}_4$ and $\mathrm{Al}(\mathrm{C}{}_2\mathrm{H}{}_5){}_3$ is essential for chain growth.
3. CTermination by combination gives a dead chain with initiator-derived fragments at both ends.
4. DShort and long branches arise through chain transfer to polymer, such as back-biting.