Which choice provides the most effective introduction to this paragraph? 

A) Montessori dedicated herself to travelling the world and preaching the benefits of childcentered education. 

B) Montessori’s first school enrolled 50 students from poor working families. 

C) Montessori did not have a particularly nurturing relationship with her own son, Mario, who was raised by another family. 

D) As the Montessori method was gaining a foothold, Europe was undergoing dramatic social and political change.