The correct answer is A) between 34 and 63 knots. According to the Saffir-Simpson Hurricane Wind Scale used by the National Hurricane Center, a tropical storm is a tropical cyclone that generates sustained wind speeds between 34 and 63 knots (39 to 73 mph). This is the wind speed range that defines a tropical storm, which is stronger than a tropical depression (20-33 knots) but weaker than a hurricane (64 knots or higher). The other options are incorrect because B) 20-33 knots defines a tropical depression, not a tropical storm, and D) over 63 knots describes a hurricane, not a tropical storm.