B1.part1.rar -

Because .rar files with this naming convention are often split parts of a larger set, "Part 1" usually contains the foundation of a course:

The first half of the textbook, focusing on core grammar like present/past tenses and basic modal verbs. B1.part1.rar

Highly popular for grammar and vocabulary practice. Because

Exercises for self-study and the corresponding keys to check your work. B1.part1.rar

Often split into parts for specific regional curricula.

Frequently distributed as multi-part archives for easier downloading. ⚠️ A Note on Split Archives

The first set of listening tracks for classroom or lab practice.