Sonet: is a standard for optical transmission that currently operates at terabit per second speeds is almost identical to the itu-t standard, synchronous digital hierarchy (sdh) uses existing copper cabling and the pstn network refers to sprint overall network is not currently available, even in large cities

The correct option to the following question is an option (B).

Explanation:

SONET is also known as the Synchronous Optical Network which is the optical fiber that is used to establishes digital communication and it is also the transmission system, it was evolved in the 1980's by the Bellcore in United States.

It is the subset of SDH and SDH is also known as the  Synchronous Digital Hierarchy that is used for the transmission and transport the communication signals

answerthe above statement is (true);