单项选择题

Directions: In this section you will hear two mini-talks. At the end of each talk, there will be some questions. Both the talks and the questions will be read to you only once. After each question, there will be a pause. During the pause, you must choose the best answer from the four choices given by marking the corresponding letter with a single bar across the square brackets on your Machine-scoring Answer Sheet.
This passage is mainly about______.

A. our modern road-building methods
B. Roman tools and machines
C. how the Romans built highways
D. how to dig stone with fire and water