The answer is d: 15,000 person-years of cycling per fatality. The Cyclist's Touring Club has about 60,000 members. On average, there are about 3 to 5 member fatalities per year. That means, if the average CTC member rides 15,000 years, he'll reach a 50% chance of a fatal bike accident. (For less enthusiastic cyclists in Britain, a similar computation gives roughly the same answer.) 7
So even in Britain, where cycling is more dangerous per hour than motoring, it seems it's not very dangerous in any absolute sense.