Answer:
c. used a Teletype or TDD machine for telephone calls
Explanation:
A video relay service (VRS) is a video telecommunication service which enables any individual with hearing disabilities or speech impairment to communicate over video telephones using American Sign Language (ASL).
Before video relay services were developed, people who use sign language used a Teletype (TTY) or Telecommunications Device for the Deaf (TDD) machine for telephone calls. The TTY or TTD enables individuals with disabilities or speech impairment to communicate with others with or without disabilities through the use of a keyboard.
Robert Weitbrecht invented the first Teletypewriter (TTY) in 1964.
The TTY or TTD is strictly text based while its modified version, VRS is video based.
