From

Kaplan 800:

Some analysts warn that, if the "numbers prove to be accurate", the entire SS system _________ in danger of failing.

(D) would continue to be

(E) will continue to be

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I would like to know why D is incorrect. Per MGMAT, "If she ate pizza tomorrow, she would fall sick" is a correct sentence. Then, why isnt D? (If hypothetical event, X would Y).

Perhaps "prove to be accurate" is not in the hypothetical-past tense? Should it be "numbers were accurate" to make D correct? or perhaps "if someone proved the numbers to be accurate"?

Another reason why would seems appropriate here is that this is a prediction and doesn't seem 100% certain given the statistical nature.

Can someone please provide a clear rule of thumb on when to use will and when to use would, for a sentence:

If X (in the future), then Y would/will Z