GMAT Sentence Correction (SC) | Re: would vs will(absolute rules)

I'm always hesitant to address anything in grammar as an absolute rule, because languages are always full of exceptions! However, I feel fairly confident answering these:

1. Your examples are reversed. It should be "If he eats, he will fall sick" and "If he ate tomorrow, he would fall sick." The first is a simple conditional, and the second uses the hypothetical subjunctive. We use "will" with respect to the present. When we use the past tense form to indicate a hypothetical,
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