Final answer:
The Altamont Free Concert in December 1969, marked by the stabbing of an audience member, is considered the end of the 60s 'peace and love' ethos, contrasting the earlier idealism of Woodstock. The correct option is b.
Step-by-step explanation:
The Rock and Roll concert in December of 1969 that marked a symbolic end to the "peace and love" ethos of the 60s, after an 18-year-old audience member was stabbed to death by a member of the Hell's Angels, was the b) Altamont Free Concert. This event is often contrasted with the cultural high note set by Woodstock earlier that year, which represented an idealistic apex of the youth counterculture movement, featuring peace, music, and widespread drug use.
While Woodstock was a peaceful event and became an iconic moment in rock 'n' roll history, the violence that erupted at Altamont was seen as the end of an era, reflecting the disillusionment and darker aspects of the counterculture.
The turn of the decade saw the youth's bright optimism of the 60s begin to falter, with rising violence, political scandals, and the death of notable figures like Jimi Hendrix and Janis Joplin, symbolizing a sobering shift in American culture and the start of a more cynical era in the 1970s.
Hence, Option b is correct.