For step-growth polymerisation of an equimolar mixture of a diamine and a diacid, use the Carothers equation ${\overline{X}}_n=1/(1-p)$, where $p$ is the fraction of functional groups reacted. Which statements are correct?

1. AAt $p=0.98$ the number-average number of monomer units per chain is 50.
2. BA radical initiator is needed to start each chain.
3. CMonomers are used up early, and high molar mass chains appear only when $p$ is very close to 1.
4. DRemoving the small by-product (water) from the mixture helps push the reaction to high $p$.