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 example. I think he should re-take GMAT again ASAP. Here this is a mere suggestion.
In another case, --- I feel that the erring politician should meet his waterloo this time for hobnobbing with anti-socials. -- here this is a wishful thinking.
Therefore, 'should' may not always point to compulsion as in the case of 'ought to' or 'must'
Canadian scientists have calculated that
one human being should be struck every nine years by a meteorite, while each year 16 buildings can be expected to sustain damage from such objects.
(A) one human being should be struck every nine years by a meteorite
(B) a human being should be struck by a meteorite once in every nine years
(C) a meteorite will strike one human being once in every nine years
(D) every nine years a human being will be struck by a meteorite
(E) every nine years a human being should be struck by a meteorite
let's drop A and C for using the unseemly One human being suggesting somewhat oddly that one same human being is struck by a meteorite every nine years once. Let's us eliminate B and E for the wrongful suggestion by using the inapt 'should. D remains
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Thank you Daagh for your time on GMAT Club and all your contributions! Thank you for everything you did!Your work will remain a great tribute to you here on GMAT Club!
-bb