单选题 .  Sea rise as a consequence of global warming would immediately threaten that large fraction of the globe living at sea level. Nearly one-third of all human beings live within 36 miles of a coastline. Most of the world's great seaport cities would be     21    : New Orleans, Amsterdam, Shanghai, and Cairo. Some countries—Maldives Islands in the Indian Ocean, islands in the Pacific—would be inundated. Heavily populated coastal areas such as in Bangladesh and Egypt,     22    large populations occupy low-lying areas, would suffer extreme     23    .
    Warmer oceans would spawn stronger hurricanes and typhoons,     24    in coastal flooding, possibly swamping valuable agricultural lands around the world.     25    water quality may result as     26    flooding which forces salt water into coastal irrigation and drinking water supplies, and irreplaceable, natural     27    could be flooded with ocean water, destroying forever many of the     28    plant and animal species living there.
    Food supplies and forests would be     29    affected. Changes in rainfall patterns would disrupt agriculture. Warmer temperatures would     30    grain-growing regions pole-wards. The warming would also increase and change the pest plants, such as weeds and the insects     31    the crops.
    Human health would also be affected. Warming could     32    tropical climate bringing with it yellow fever, malaria, and other diseases. Heat stress and heat mortality could rise. The harmful     33    of localized urban air pollution would very likely be more serious in warmer     34    . There will be some     35    from warming. New sea-lanes will open in the Arctic, longer growing seasons further north will     36    new agricultural lands, and warmer temperature will make some of today's colder regions more     37    . But these benefits will be in individual areas. The natural systems—both plant and animal—will be less able than man to cope and     38    . Any change of temperature, rainfall, and sea level of the magnitude now     39    will be destructive to natural systems and living things and hence to man as well.
    The list of possible consequences of global warming suggests very clearly that we must do everything we can now to understand its causes and effects and to take all measures possible to prevent and adapt to potential and inevitable disruptions     40    by global warming.21.