I would think that you would have to do 42/2=21Hz, but I'm not sure...
It takes a noun and a verb to make a complete sentence.
There isn't a single verb in a), b), or c).
"Affords" is the verb (predicate) in d)., the only complete sentence.
These are all caused by tectonic plate movements. Some areas of the globe are more susceptible to these disasters because they are on or near a fault line where the Earth’s tectonic plates rub against one another, slip beside and under each other, or collide. The places near fault lines are more likely to see earthquakes, tsunamis, and volcanic activity.
I think the answer would be letter B.
