Besides enzymatic means, physical stress can also be used for cleaving the DNA. Which of the following statements is true?

a) Sonication, needles, syringes, etc all come under the category of physical stress

b) In physical stress, there are no chances of contamination

c) The ends obtained have unique sequences

d) They are less effective than DNase treatment

Explanation: Physical stress methods are used to cleave the DNA randomly and it also generates non-unique ends as the DNase treatment. These include the use of sonication methods, needles and syringes. There are chances of contamination from the metal probes used in the setup used.