Vancouver is the best place to live in the Americas, according to a quality-of-life rankin

g published earlier this month. The city regularly tops such indexes as its clean air, spacious homes and weekend possibilities of sailing and skiing. But its status as a liveable city is threatened by worsening congestion(拥挤). Over the next three decades, another 1 million residents are expected to live in the Greater Vancouver region, adding more cars, bicycles and lorries to roads that are already struggling to serve the existing, 2. 3 million residents. A proposal by Vancouvers mayor seeks to prevent the worsening conditions. Upgrades would be made to 2, 300 kilometres of road lanes, as well as bus routes and cycle paths. Four hundred new buses would join the fleet of 1, 830. There would be more trains and more "seabus" ferry crossings between Vancouver and its wealthy northern suburbs. To get all that, residents must vote to accept an increase in sales tax, from 7% to 7. 5%. Polls suggest they will vote no. Everyone agrees that a more efficient transport system is needed. Confined by mountains to the north, the United States to the south and the Pacific Ocean to the west, Vancouver has spread in the only direction where there is still land, into the Fraser Valley, which just a few decades ago was mostly farmland. The road is often overcrowded. Yet commuters suspicion of local bureaucrats may exceed their dislike of congestion. TransLink, which runs public transport in the region, is unloved by taxpayers. Passengers blame it when Skytrain, the light-rail system, comes to a standstill because of mechanical or electrical faults, as happened twice in one week last summer, leaving commuters stuck in carriages with nothing to do but expressing their anger on Twitter. That sort of thing has made voters less willing to pay the C $ 7. 5 billion in capital spending that the ten-year traffic upgrade would involve. Despite the complaints, Vancouvers transport system is a decent, well-integrated one on which to build, reckons Todd Litman, a transport consultant who has worked for TransLink. "These upgrades are all-important if Vancouver wants to maintain its reputation for being a destination others want to go to," he says.

The biggest problem threatening Vancouver as a liveable city is______.

A．increasing congestion

B．climate change

C．shortage of land

D．lack of money