Answer:
More than 50 studies were conducted.
The US Public Health Service was responsible for part of the study.
Step-by-step explanation:
If more than 50 studies have been conducted on the relationship between water fluoridation and cancer risk, then the results of this study are already repeated in others, which proves its accuracy. In addition, this means that this relationship has strong scientific evidence to testify that the results are correct.
In addition, if the US Public Health Service was responsible for part of the study, then the study was conducted by a responsible institution with professional subject matter experts who can establish a serious and scientifically sound study.