L2C 李梦媛 unit 17 作业

9. a cheaper alternative to supervision {A- video surveillance}

解析：这道题可以在文章D段中找到 原句是这样的 It is also a cheaper alternative to other forms of security and supervision.

15. makes the firm more efficient. {C- tracking devices}

解析：这道题可以在文章F段找到 原句是 According to employers, vehicle tracking is used to increase efficiency.