The difference between "fluctuate" and "ebb and flow"?
The sentence is:
Because foreign exchange rates ebb and flow/ fluctuate, it is not always possible for exporters to know how much money they will receive from sales.
The answer is fluctuate. Can you explain why?

Question

Answer

"Ebb and flow" is like the action of ocean tides. They're regular and predictable.  "Fluctuate" means to change slightly, but this is not predictable.

Because the results are uncertain, the correct answer is "fluctuate".

Answer

Ebb and flow, and Fluctuate are interchangeable. However, fluctuate is used more for rise vs decline, whereas ebb and flow is used more for 'back and forth'