有關現在完成式既問題詢問一下

Jenkin,
你有冇發覺類似問題問過好多次，你都答過好幾次﹖

假如你只是交代最後的情況
Tom has left his room.也不是錯的-因為在你講/報告這句時他已經是離開(不在)房裏。
至於要交代他在之前又進又出或者想詳細表達已發生的過程，就不是用一句或者單用一種tense的動詞組便可以的，而且表達的深度亦可以有不同。

例如:

He has been in and out of his room and he has left.
[全以現在完成式來表達他的情況...表示在之前的一段短時間內發生了的]

He left his room before and came back, and now he has left.
[不要以為now便一定是-ing的現在進行式動詞(那是小學程度的習作)，現實生活的英語now可以指你說話的當時情況"他已經走了/不在"便可以now配present perfect tense；而之前發生的出出入入便用simple past tense來描寫發生在過去了的情形，以對比現在的"已走了"的狀況。

因此要看你作為講者/作者希望表達的時空感覺和交代的細緻度或重點是甚麼，另外可能還有更多可以表達他出去-回來-再出去了的不同寫法，以上只是想像到的可能講法。

希望

The present tense is used for an action just concluded when the resulting state is still present,eg:-
Despite the previous first time, Tom has left his room twice.
Tom has left his room; he is able to count it as the second time.
Tom has left his room (since); that is to be counted as the second time.
This leaving was working out all right (just) a moment ago, but now Tom has left his room finally.
With activity completed in the immediate past, (just,since) are often used; and
note that just now=up to now, is an adverbial of the present:-eg:-
Tom has left his room just now.
or Tom has left his room for the second time.

2014-06-04 16:01:18 補充：
This tense is usual with already:-eg:-
He has already left his room after in and out.
This morning can be used with a present perfect depending on the time the statement is made,eg:-
He has left two times this morning (said during the morning).