was or were

成句英文句子應該寫成：
I was grateful to your help yesterday.
因為句子末段有一個yesterday的字樣，意即昨天。
I 這個字後面，通常都是用was，好少會用到were呢個字。I 係得一個人咋嘛。

正如你所說, I (be ) grateful to your help yesterday. 一句中,
是不能用were 的. 第一, I 是單數, 而were 是複數動詞, 根本
唔match. 第二, I were, 是用於假設性語氣, 例如: If I were
a bird, I could fly to USA. 而你這句很明顯地, 是一句表達感
謝的句子. 所以, 就不可以用were.

You should change this sentense into:

I was grateful to your help yesterday.

Because single in past tense uses 'was' and puarl in past tense uses 'were'.

I would like to know whether can we use were as the past tense of be when the situation is I (be ) grateful to your help yesterday.
I, he, she & it - use was as past tense.
You, they, these - use were.
Only in one occation you can use were for I, that is:
If I were you. 因這是不可能的事, 故英語用一錯的tense來強調.

2008-01-18 17:07:21 補充：
only in one occasion ...............occation 打錯應是 occasion