Some advocates for Tibet, Darfur, and the spiritual practice Falun Gong, planned to protest the April 9 arrival of the torch in San Francisco. China had already requested the torch route in San Francisco be shortened. On April 7, 2008, two days prior to the actual torch relay, three activists carrying Tibetan flags scaled the suspension cables of the Golden Gate Bridge to unfurl two banners, one saying "One World, One Dream. Free Tibet", and the other, "Free Tibet '08". Among them was San Francisco resident Laurel Sutherlin, who spoke to the local TV station KPIX-CBS5 live from a cellphone, urging the International Olympic Committee to ask China not to allow the torch to go through Tibet. "Sutherlin said he was worried that the torch's planned route through Tibet would lead to more arrests and Chinese officials would use force to stifle dissent." The three activists and five supporters face charges related to trespassing, conspiracy and causing a public nuisance.

Answer this question, if possible (if impossible, reply "unanswerable"): Three protester climbed what to hang two banners on April 7, 2008?
Golden Gate Bridge