The series by Biboletova et al. is one of the most widely used English textbook series in Russian schools. Because it’s so common, the GDZ (Готовые Домашние Задания) or "solved homework" materials for it are extensive and highly rated by students.
Unlike some simple answer keys, top platforms like Skysmart provide detailed breakdowns of why an answer is correct, which helps with actual learning rather than just copying.
Most Biboletova GDZs include full translations of the texts and dialogues, which is a lifesaver for students struggling with vocabulary.