If scientists were trying to construct recombinant dna molecules, how would they do it?

Constructing recombinant DNA or rDNA scientists should combine both DNA from two different species.  Based on study, rDNA is possible if both DNA that should be combined should have the same chemical structure. Most o the DNA do have the same structure they only differ in nucleotide sequence. 

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i think that c)gold was found there

but i am not sure