which Debian installation package files are loaded?

Which file should be edited to select the network locations from which Debian installation package
files are loaded?

A.
/etc/dp kg/dp kg. cfg

B.
/etc/apt/apt.conf

C.
/etc/apt/apt.conf.d

D.
/etc/apt/sources.IIst

E.
/etc/d p kg/d s e I e ct. cfg