GMAT Sentence Correction (SC) | Canadian scientists have calculated that one human being

It is doubtful whether 'will' always means a certainty. For example, take this case:
Seeing the binge with which Yellen is eager to go, analysts think that FED will raise the rate yet again as early as March this year.

Here, 'will' signifies more speculation or at the most some anticipation or expectation. 'Will' is often used for the futurity of the event rather than for the surety of the event.

The next point. 'Should' is often a kind of suggestion and in some cases even dreaming. For
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