One of the inadequacies of DL is a good means of explaining why an answer is wrong. It would be great if there was one Forum discussion page organized by lesson topic, with translations that have been reported as "should be correct" with explanations. Either 제가 or 저는 could be used to translate this sentence depending on the situation. One person may claim to have a large library, because he buys a book when he feels like reading. His friend, by contrast has a different method. and the Korean representation to show that contrast would be 저는 or 나는.