Hello Hyomin, When you are actually in the class you would say 'I haven't brought my book.' because this action has an effect now. You haven't got your book so you need to look at another students book. (This is British English) I suspect that in American English they would use the past simple. (Your first sentence!) The present perfect is one of the few pieces of grammar which are not common in British and American English. Hope this helps Bob

In my opinion, "I didn't bring my English book." is correct. To understand it simply, people usually say "I forgot my English book" not "I've forgotten my English book." If you want to have a further look, it's also because the simple past tense indicates things that happened and finished. Meanwhile, present perfect tense is used for things that happened in the past and it might happen in the future. Hope it's useful for you.

In this case, the 2nd "I haven't brought my English book" is probably more correct as the subject (English book) is still significant at the present time. If it was after the the lesson, then "I didn't bring my English book" would be more correct as you would be recalling what had happened at the time of the English class. Hope that helps!

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