For what does the world owe Almon Strowger a debt of gratitude?

Option C

An automatic telephone exchange is a centralized place from where all telephone connections are connected to each other indirectly. It has a number of electromechanical switches in it that are controlled by dialled pulses. An exchange will always be situated at the center of a population.

An automatic Strowger telephone exchange, there can be two types of answering methods -

(1) Pre-selection and

(2) Line finding.