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.
Women coulnd’t study medicine at universities (65) ________ the 19th century and they only began to gain equality with male doctors in the 20th century.