The word "assume" (Line 5, Para. 1) could best be replaced by______.

A．it is composed of people themselves
B．it is one of the social institutions
C．it is something hard to understand
D．it involves many different social customs

A．be able to behave politely to other people
B．become an accepted member of his society
C．know how to farm or herd cattle
D．approach his society's gods and receive help from them