PATHOLOGY

Detailed explanation-1: -Answer and Explanation: The correct answer is D. restriction enzymes. Restriction enzymes, which are produced naturally by bacteria as a defense against viruses, recognize and cut DNA into pieces at specific sequences.

Detailed explanation-2: -SmaI is an example of a restriction enzyme that cuts straight through the DNA strands, creating DNA fragments with a flat or blunt end. Other restriction enzymes, like EcoRI, cut through the DNA strands at nucleotides that are not exactly opposite each other.

Detailed explanation-3: -Restriction enzymes, found naturally in bacteria, can be used to cut DNA fragments at specific sequences, while another enzyme, DNA ligase, can attach or rejoin DNA fragments with complementary ends.