Textbook supporting answer book: The advanced comprehensive course of practical English in the 20th century is published, with detailed answer books, including the answers to exercises after each lesson.
On the Internet: Now many online resources can provide answers to after-school exercises in various textbooks. You can try to search for the keyword "answers to after-school exercises in the 3rd edition of 2 1 century practical English comprehensive course" on some online education platforms, learning forums or related education websites.