一、present perfect tense

构成：

主语+助动词（have/has）+动词的过去分词（have/has been/done）

过去分词变化：

1、一般动词，+”-ed”；例—-work/worked、visit/visited
2、以不发音的”e、ue”结尾的动词，+”-d”；例—-live/lived
3、以”辅音字母+y”结尾的动词，将”y”变”i”，再加”-ed”；例—-study/studied、cry/cried、try/tried
4、”重读闭音节”结尾且末尾只有一个辅音字母（w、x、y除外），辅音字母前只有一个元音字母，先双写辅音，再加”-ed”；例—-stop/shopped、plan/planned
5、以c结尾的动词，变c为ck，再加”-ed”；例—-picnic（野餐）/picnicked、traffic（交通）/trafficked

use Present perfect tense？

1、in the recent past——present
2、started in the past——still happening now
3、already、ever、for、just、lately、never、recently、since、yet
already：affirmative statement——例：The boy has already come home
yet:negative statement—-例：I haven’t heard anything from him yet
for:for+a period of time—-例：we haven’t seen him for two days
since:since+a point in time—-例：we haven’t seen him since last Monday
4、actions that completed only a short time ago
例子：The police have just finished searching the area
5、repeated actions
过去到现在、过去发生到现在继续发生的、特定的词语、刚刚完成的、重复的