Which of the following statements is correct?

Insulin consists of two short polypeptide chains: chain A and chain B, that are linked together by disulphide bridges. Insulin is synthesised as a pro-hormone in all mammals including humans. Proinsulin contains an extra stretch called the C peptide. Genetically engineered insulin is produced using genetically engineered E. coli. Insulin cannot be administered orally as it is a protein hormone and gets digested in the alimentary canal before being absorbed.