Recombinant DNA used to produce human insulin protein in bacterial cells. This procedure relied on cloning a human gene into a plasmid at a location directly adjacent to a bacterial promoter sequence. Why not use the promoter from the human insulin gene for this application?

Promoter from the human insulin gene has large intron and limited tRNAs for complete expression

Explanation:

A bacterial promoter sequence is used as it is made intron free which is not the case with human gene as it contains large introns. Hence an intron free version is created as cDNA. cDNA is made out of mRNA and has no regulatory region. Also, the bacterial promoter sequence contains sufficient ribosome-binding site, and terminator sequences with tRNAs in number enough for complete expression

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the answer to your question is b