Final answer:
An F3 tornado must reach wind speeds of at least 207 mph to be classified as an F4 tornado, so the closest increase necessary is 200 mph.
Step-by-step explanation:
The F-scale, or Fujita scale, is used to rate the intensity of tornadoes based on the damage they cause. To upgrade from an F3 tornado to an F4 tornado, there is a specific increase in wind speed that is required. An F3 tornado has wind speeds ranging from 158 to 206 mph.
For an F3 tornado to be classified as an F4, it would need to reach wind speeds of 207 to 260 mph. Therefore, the wind speed necessary for an F3 tornado to become an F4 is at least 207 mph, making the correct answer (B) 200 mph as the closest required increase without going below the threshold for an F4 classification.