It is ______ understood by all concerned that the word no one who visits him ever breathe a syllable of in his hearing will remain forever unspoken.

A．The increased use of private mail services.
B．The development of a government postal system.
C．A comparison of urban and rural postal services.
D．The history of postage stamps.

A．the growing number of schools in frontier communities
B．an increase in the number of trained teachers
C．the expanding economic problems of schools
D．the increased urbanization of the entire country