视频对白：
On an average of ten different surveillance cameras. Now, it's hundreds.
平均会被10个监视器拍下。现在是上百个。
Bad for privacy, but good for us.
无隐私可言，但对我们有利。

今天我们要学习的词组为：on an average

意为“平均起来，一般说来”。

例句：
1. In American homes, television sets were on an average of 42.7 hours per week.
美国家庭里的电视机平均每星期要开42.7小时！

2. Each quarry on an average employs about 120 workers.
每座矿山平均雇佣120个工人。