(d) : X-rays crystallography is a technique which is used to study of binding protein on regulatory DNA sequence. In this technique, X-rays pass through a crystal of a substance and form a diffraction pattern. With the help of this technique, the arrangement of atoms in the molecular structure of enzymes, proteins, DNA, etc. can be studied. Wilkins, Watson and Crick used this technique to determine the molecular configuration of double helix of DNA.