【单选题】

Watch out! Here comes London MayorBoris Johnson riding a bicycle from his new bike hire plan. "What we’ve put in is a new form of public transport. These bikes are going to belong to everybody. "

More than 12000 people have signed up for the plan. They each receive a key at a cost of three pounds, with costs at one pound for a 24-hour membership, five pounds for seven days, and 45 pounds for an annual membership.
John Payne, a London teacher who cycles a lot, is among the first to use the system. "It’s very comfortable. For people who don’t cycle much I think it’ll be very useful.But for people who cycle regularly, they are possibly a bit slow.But they’re perfect for London streets, very strong. I think they’ll be very widely useD、"
And Johnson says it’s of good value. "I think it’s extremely good value. The first half hour is free. If you cycle smart and you cycle around London--most journeys in London take less than half an hour, you can cycle the whole day free. " Some 5 000 bikes are currently available at over 300 docking stations (租车点) in central London. Johnson says the city will gradually expand the system, "Clearly one of our ambitions is to make sure that in 2012 when the world comes to London, they be able to use London hire bikes to go to the Olympic stadiums. \
According toBoris Johnson, one can cycle around London the whole day free ______.
A、because most journeys take less than half an hour
B、because the bike hire is free for the fires time
C、if one can arrange his London tour in a smart way
D、if one is physically strong enough