Given a scientific passage and an answer, generate a question for the given answer.

[EX Q]: Passage: Restriction enzymes or restriction endonucleases are prokaryotic enzymes that recognize and cut DNA at specific sequences, called restriction sites. It is believed that they evolved as a defense mechanism against foreign DNA, such as viral DNA. Over 3,000 restriction enzymes have been identified. Some of the more common restriction enzymes are shown in the table below, where up and down arrows show the sites of cleavage. Restriction enzymes are named based on the prokaryotic organism they are isolated from. For example, those isolated from Escherichia coli would begin with Eco. As the Table below shows, digestion with the restriction enzymes will result in overlapping or blunt ends. EcoRI produces overlapping "sticky" ends: the enzyme cleaves between the G and A on both strands. On the other hand, SmaII restriction enzyme cleavage produces "blunt" ends. The enzyme cleaves between the G and C on both strands. Answer: dna
[EX A]: Restriction enzymes or restriction endonucleases are prokaryotic enzymes that recognize and cut what at specific sequences?

[EX Q]: Passage: Cutting down on the use of chemical fertilizers is one way to prevent dead zones in bodies of water. Preserving wetlands is also important. Wetlands are habitats such as swamps, marshes, and bogs where the ground is soggy or covered with water much of the year. Wetlands slow down and filter runoff before it reaches bodies of water. Wetlands also provide breeding grounds for many different species of organisms. Answer: dead zones
[EX A]: Cutting down on the use of chemical fertilizers and preserving wetlands are ways to prevent what "unlivable" regions in bodies of water?

[EX Q]: Passage: Smoking is the major cause of chronic respiratory disease as well as cardiovascular disease and cancer. Exposure to tobacco smoke by smoking or by breathing air that contains tobacco smoke is the leading cause of preventable death in the United States. Regular smokers die about 10 years earlier than nonsmokers do. The Centers for Disease Control and Prevention (CDC) describes tobacco use as "the single most important preventable risk to human health in developed countries and an important cause of [early] death worldwide. " Simply stated: Stopping smoking can prevent many respiratory diseases. Answer: smoking
[EX A]:
What is the major cause of chronic respiratory disease as well as cardiovascular disease and cancer?