A state government study surveyed a representative sample of child-care centers about childhood illnesses. Which statement BEST explains what makes the sample representative?
A
Every child-care center in the state participated in the study.
B
Every child-care center in the state had an equal chance of participating in the study.
C
Every child-care center was asked a series of randomly selected questions.
D
Every child-care center that participated must have reported childhood illnesses to the state.