關於現在完成式問題想問下

07:00--I have sent
07:05--received ?
07:30--I have sent=I was sending a letter to Mary a moment ago (07;05-07:00) but now it has stopped and received.
The above shows (1)For an action just concluded when the resulting state is still present.
With activities completed in the immediate past, just is often used,eg:-The letter has just sent.
Note that just is an adverbial of the present, just now,a little time ago, is an adverbial of the past and the verb used with it will be a past tense, eg:-The letter sent just now.
(2) For the duration of an action begun in the past and continuing to the present and possibly to the future, eg:-I have sent Mary for a letter just (07:30-07:00=00:30) minutes ago.
(3) When the time of the action is indefinite, eg:-
I have sent this letter before,
where the time is indefinite.

You may say " I have sent Mary an email ", or

" I sent Mary an email at 7 o'clock "

when time is indicated, simple past tense is usually used, when time (or date) is not indicated present perfect tense is usually used.

You may say " I have sent Mary an email ", or

" I sent Mary an email at 7 o'clock "

when time is indicated, simple past tense is usually used, when time (or date) is not indicated present perfect tense is usually used.

我在七點鐘發咗電郵給.............. .

我已經發咗電郵給.............. .

2014-02-21 17:24:04 補充：
I have sent an email to Mary 與I have sent Mary an email 兩句意思相同。