Hello. Please help! Situation 1. I read a book last night. It was about chemistry. Situation 2: I'm reading a great book. It's about chemistry. I know the past tense tell us about the past, but in situation one, why should I use the past tense? Even if I hadn't read the book, the book will still be about chemistry, isn't it a fact? Why can't we use the present tense? While for situation two, I think it makes sense to me. Please explain! Thanks!