英语的tenses。

怎样分出simple present tense
simple past tense
simple future tense
present perfect
past perfect
future perfect
有什么关键词吗或是怎样应用呢？？？
帮帮我吧！！！

simple present tense
一般现在时：is/am/are,或者动词原形.
关键词:often,always,sometimes,every day.
举例:I go to school everyday. (我每天都上学)

simple past tense
一般过去时: was/were,或者动词过去式.
关键词:yesterday, last month, last year, 反正和过去有关的词汇都是.
举例: I finished my homework yesterday.(我昨天做了家庭作业)

simple future tense
一般将来时: will/should+动词原形..或者am/is/are+going to do ....
关键词:tomorrow, next month, next year, next week,和将来有关的词汇都是.
举例:I will get up at 6:00 tomorrow.(我明天六点要起床)

present perfect
现在完成时:has/have+动词过去分词形式.
关键词: already,(已经,用于肯定句) yet,(还没,用于否定句) so far(到现在为止) since that day(从那天起)
举例:I have already finished my homework.(我已经作完了家庭作业)
I haven't finished my homework yet.(我还没做完家庭作业)

past perfect
过去完成时: had+动词过去分词形式.
关键词: by that day,(到那天为止) until that day, (直到那天)
这种时态用得不多..只要看得懂就行了.
举例:I had travelled to three countries by the year of 20.(我20岁以前去过3个国家旅行)

future perfect