In 1988,the Canadian Federal Government Raised the Speed Limit to 110

In 1988,the Canadian federal government raised the speed limit to 110 km/h.Then,in 1996,individual provincial governments were given the choice to decide the highway speed limit in their own provinces and thus many raised it to 120 km/h.Proponents and critics of the law have looked at the number of traffic deaths per 1000 kilometres driven on the highways between 1988 and 1998 to see whether the law had any impact on traffic deaths.What type of design is this?

A) One-shot case study
B) Equivalent time series design
C) Pretest-post-test one-group design
D) Interrupted time series design
E) Solomon four-group design