Student or Learner
Tornadoes occur throughout the world, but for reasons scientists are not fully able to -------, the great majority occur in the USA.
A) adopt B) allot C) sustain D) discern E) yield
I think D
Of the answers on offer, D is the one that is not impossible, though it is not very natural.
C doesn't work for me- how can you sustain reasons you don't know?
A better answer would have been explain.