Which of the following is the maximum standard distance allowed to connect a customer via an ISDN line?

Which of the following is the maximum standard distance allowed to connect a customer via an
ISDN line?

A.
6,000 feet (1,828.8 meters)

B.
8,000 feet (2,438.4 meters)

C.
12,000 feet (3,657.6 meters)

D.
18,000 feet (5,486.4 meters)