tense

0Hi,02br
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00Please tell me if what I think is correct.02br
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01i00By the time we arrive, Jane 1) will be gone/2) will have been gone/3) would be gone. 02i02br
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00I think nos. 1 and 2 are both correct, except that no.2 expresses more in terms of its activity in a certain duration; but no. 3 would be wrong in that it expresses present time.02br
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01i00We agreed that they 01u00can/could02u00 go ahead and use the computer.02i02br
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00I think with the words like 'agreed' or 'decided', it is correct to use both 'can' and 'could' in that what is agreed doesn't necessarily need to reflect the time frame in the main clause, in this case being the sentence with the verb 'agreed'. To me, 'can' denotes more certainty. The situation doesn't warrant the tense change. Right? 0-