Because .rar files with this naming convention are often split parts of a larger set, "Part 1" usually contains the foundation of a course:
Exercises for self-study and the corresponding keys to check your work. B1.part1.rar
Curated lists of "Key Words" updated for modern usage (e.g., replacing 'floppy disk' with 'app'). 🛠 Common Resource Sets Because
The first set of listening tracks for classroom or lab practice. B1.part1.rar