Find the incorrect statement.

Statements related to human insulin are given below. Which statement$(s)$ is/are correct about genetically engineered insulin?
$(a)$ Pro-hormone insulin contains an extra stretch of $C$-peptide.
$(b)$ $A$-peptide and $B$-peptide chains of insulin were produced separately in $E. coli$,extracted,and combined by creating disulfide bonds between them.
$(c)$ Insulin used for treating diabetes was extracted from cattle and pigs.
$(d)$ Pro-hormone insulin needs to be processed for converting into a mature and functional hormone.
$(e)$ Some patients develop allergic reactions to the foreign insulin.
Choose the most appropriate answer from the options given below:

Which of the following genetically engineered microbes is used in the scavenging of oil spills by digesting hydrocarbons of crude oil?

Genetically engineered human insulin is manufactured by the use of

Which of these is used as a vector in gene therapy for $SCID$?

Genetically engineered insulin can be obtained by