In 1673, letters were sent from New York and Boston, and vice versa ____ a month.

* Hướng dẫn giải

Dẫn chứng: Then, in 1673, a monthly post was set up between New York and Boston. The service was of short duration, but the post rider’s trail became known as the Old Boston Post Road, part of today’s U.S. Route 1. William Penn established the first post office in 1683.

Đáp án đúng: A. once