Problems

0What's the difference between "this morning" and "all morning" when they are used in the present perfect sentence? which one represents a duration--from the past to now? 02br
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00I have written letters . I have been writing letters. what do they mean? i know the meaning of the second one -- i wrote letters before and still writing. but what about the first one, i think maybe it also has the same meaning as the second one's,because present perfect tense also have the same usage as the present perfect continuous tense. 02br
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00I have done my homework. does it mean i have finished my homework, now maybe i have no work to do? this sentence must have this one meaning , why? OR depends on the contexts, maybe i am still doing it, according to the usage of present perfect tense--Actions which started in the past and are still continuing . Thanks for replying!0-