[单项选择]Passage Three 　　Questions 51 to 55 are based on the following passage. 　　Some years ago industries had more freedom than they have now, and they did not need to be as careful as they must today. They did not need to worry a lot about the safety of the new products that they developed. They did not have to pay much attention to the health and safety of the people who worked for them. Often new products were dangerous for the people who used them；often conditions in the work place had very bad effects on the health of the workers. 　　Of course sometimes there were real disasters(灾难) which attracted the attention of governments and which showed the need for changes．Also scientists who were doing research into the health of workers sometimes produced information which governments could not ignore．At such times, there were inquiries into the causes of the disasters or the problems. New safety rules were often introduced as a result of these inquiries；however, the new rules came too late t
A. conditions in the work place
B. the freedom of industries in the past
C. changes in industrial production
D. the safety and health of workers and　customers