In addition, drivers could be required to pay for using particular routes at different times of the day.

Đáp án A.

Tạm dịch: …including serious air pollution, lengthy delays, and the greater risk ________ accidents: bao gồm ô nhiễm không khí nghiêm trọng, sự chậm trễ kéo dài, và nguy cơ tai nạn cao hơn.

- risk + of sth: nguy cơ, nguy hại.

Ex: Building work has a high risk of accident.