Change 的用法

1)has changed
has changed 係 Present Perfect Tense
e 一種Tense 係由 has/have + 過去分詞 組成
Present Perfect Tense 用於
(1) 已經完成但與現在仍有關聯的動作或狀態；
(2) 過去已經開始並持續到現在的動作或狀態；
(3) 經驗過的動作或狀態。
example: He has changed a short now.﹝我現在已換了一條短褲。﹞

2) is changed 同 has been changed 都係被動式" Passive Voice"
is changed 係 Passive Voice @ Simple Present Tense
has been changed 係 Passive Voice @ Present Perfect Tense
所以 is changed 同 has been changed 既分別只在於時間性
example 1: My computer is changed to a new one. (我的電腦被換成新的一部)(時間性上:永久)
example 2: My computer has been changed to a new one this mroning. (我的電腦剛於早上被換成新的一部)(時間性上:上午)
[在說這一句時,只應仍身處上午(剛發生).如你身在下午時說這一句便錯,因已過"剛發生"的時間]



以下網頁(lesson 1-37 )幫到你: http://www.npc.edu.hk/staff/~ngtungying/english_grammar/lessons/lesson01.htm

is changed~~passive voice
has changed~~present perfect tense
has been changed~present passive perfect tense