The correct answer is option A. "They only introduce supercoiling and cannot relax a covalently closed circular DNA".
Explanation:
Type II topoisomerases are enzymes that regulate the winding an unwinding of DNA during DNA replication. Basically, these enzymes are the scissor that remove the knots and tangles formed during the replication process. Is false to affirm that type II topoisomerases only introduce supercoiling and cannot relax a covalently closed circular DNA. Bacterial type II DNA topoisomerases work with the circular DNA of bacterium by changing the linking number of circular DNA by ±2.
The tricuspid valve shuts. This prevents blood from flowing backward into the right atrium while the ventricle contracts. So, your answer will be the Tricuslid Valve. Hope I helped!
