這句文法是否正確？

文法正確。可用 SVO 句法來看：

S: I

V: was

O: unable to eat and drink

unable 是個形容詞，而後面的 eat 和 drink 兩個動詞是用來修飾 unable，讓意思完整起來：不能吃和喝。

如果沒有了 eat 和 drink ，只剩 unable 的話，這句就會變成 I was unable，即「我是無能」，而不是「我不能吃和喝」的意思了。


希望幫到你。

2013-07-03 17:48:24 補充：
另外，其實 eat ''and'' drink 和 eat ''or'' drink 也有意思上的分別：
eat ''and'' drink 暗示了「同時吃和喝東西」；而 eat ''or'' drink 則暗示了「吃東西或喝東西」不會「同時」做這兩件事情。

I was unable to eat and drink.= I could not eat and drink (both in past tense)

I am unable to eat and drink= I cannot eat and drink ( both in present tense).

文法正確，I was unable to eat and drink. 表示：我不能吃和喝。

Grammatically, “and” is correct, but as a matter of fact, you can’t eat and drink at the same time, so verbally:
I can't eat or drink.

[ I am unable to eat or drink. is rather formal.]