Context: There were four major HDTV systems tested by SMPTE in the late 1970s, and in 1979 an SMPTE study group released A Study of High Definition Television Systems:

Question: How many major HDTV systems were tested by SMPTE in the late 70's?
Answer: four

Question: Who tested the four major HDTV systems in the late 1970's?
Answer: SMPTE

Question: Who released A Study of High Definition Television Systems?
Answer: an SMPTE study group

Question: In what year was A Study of High Definition Television Systems released?
Answer: 1979

Question: What was released by an SMPTE study group in 1979?
Answer: A Study of High Definition Television Systems

Question: How many major SDTV systems were tested by SMPTE in the late 70's?
Answer: Unanswerable

Question: Who tested the three major HDTV systems in the late 1970's?
Answer: Unanswerable

Question:  Who released A Study of Standard Definition Television Systems?
Answer: Unanswerable

Question: In what year was A Study of Standard Definition Television Systems released?
Answer: Unanswerable

Question:  What was released by an SMPTE study group in 1989?
Answer: Unanswerable