Et tu, San Francisco? The city’s public-transportation system, BART, closed all four of its stations in downtown San Francisco on Monday evening due to protests. Protesters were demonstrating against the agency’s decision to cut underground cellular service for three hours last Thursday night in an effort to stop a possible protest that day. BART spokesman Linton Johnson said riders “don’t have the right to free speech inside the fare gates,” and said cellphone service would possibly be cut again. He said riders’ safety had been compromised by protests over the death of a knife-wielding man on July 3 at a BART station.