have been / was

唔敢答話實啱，因為唔係好明這些句字是錯的定義，但有些是明顯錯的：

I have been studying.錯可能是因為have been studying一般不會獨立自己一句的。但同時如果這是一個問題：Have your been studying?的答答則是對的。
所以我不會說錯。不過同時如果是考究perfect tense的寫法，這句可能應該是：I have studied.

I had been studying hard.錯在用了past perfect tense的had...。理由是study hard這句意思一般是即場說的，所以不會以past perfect continuous tense來寫。另外跟上句一樣，用past perfect continous tense可能意會是還有另一情的出現。

I had been studying hard for one hour when my mother came.錯在用had been studying這past perfect continuous tense.情況是study hard這動作是持續的，came是在這持續的動作當中在過去的一點(時間)上的出現/行為。所以study hard應用present perfect continous，由之前一直做到現在，如果用past perfect的話代表在過去開始在過去已完成的一件事。
I have been studying hard for one hour when my mother came.

It had rained since yesterday錯在句子用了since yesterday表達從昨天直至現在仍下雨，所以動詞是用從以前直至現在的present perfect continous來寫。
It have been raining since yesterday.
除非這句是故事敍述或第三身旳報告才會用past tense的had been raining.
原句的had rained是被動式，即it被下雨淋了，it所指是天氣/雨本身，所以不能自己被自己動詞做。是錯的。

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I have been studying. ( you are still studying hard when you say this))

I had been studying hard. (you are no longer studying when you say this)

I had been studying hard for one hour when my mother came. = correct

It HAS rained since yesterday. OR it has been raining since yesterday ( both mean similar and it is still raining when you say this)