A、It is a city suffering from noise. B、It is a city full of discrimination and injustice. C、It is the city where the AIDS crisis

"The San Francisco Bay Area is the playpen of counterculture," said Time Magazine in 1986. Indeed, San Francisco has never been a city to stay quiet in times of injustice, and this was never more clear than during the beginning of the AIDS crisis. A new exhibition "Life and Death in Black and White" captures the emergence of AIDS activism in San Francisco through civil disobedience and militant action. All 17 photographs on view were taken by five odd photographers in the 1980s and 1990s. The exhibition is equal parts art and history—its photographic memories are displayed chronologically, with text providing some context for those unfamiliar with the struggles of the time. The collection provides climactic moments of activism, for example, when citizens chained themselves to the doors of the Federal Building on UN Plaza, to make themselves heard. From a blockade on the Golden Gate Bridge to an ACT UP demonstration, the exhibition highlights the pain, the rage and the bravery involved in the fight for AIDS awareness. The crisp and clean black and white photos bring a feeling of control and simplicity to a time of chaos, when an unnamed disease targeted half of the city’s gay men and government agencies seemed incapable of listening. Yet in the darkest times come the brightest inspirations, as thousands of San Franciscans rose to the challenge and fought for their voices to be heard.
19. What can be inferred about San Francisco?
20. What is the theme of the exhibition "Life and Death in Black and White"?
21. What can we learn about the exhibition?