Answer:
In the given case, for the researcher to succeed, there is a need to place the gene next to the promoter sequence, which gets expressed in the mammary cells. The sequences of DNA, which illustrate that where the transcription of a gene by the RNA polymerase initiates is known as the promoter. These sequences are generally situated at the 5 prime terminals of the initiation site of transcription or are situated directly upstream.
The answer would be between b and d but i would go with d
