Answer:
D. DNA Contains the genetic code / instructions for the cell and the living organism they build
Step-by-step explanation:
DNA and RNA are nucleic acids that contain the genetic information so that a cell knows exactly what proteins it should make, what function it should serve.
Why not A: DNA and RNA don't strictly build cellular proteins; that job is up more to the ribosome, tRNA, and mRNA. While this could be acceptable, it's not as good an answer as D.
Why not B: This is incorrect.
Why not C: DNA and RNA don't do any of the dirty work of fighting off intruders; that's the job of the immune system, building antibodies, eating the viruses with white blood cells, and using the epidermis as a barrier to keep harmful things out.