题干

右图是某群落中甲、乙两个种群的增长速率随时间变化的曲线,下列叙述不正确的是(  )

A:甲、乙种群可能为竞争关系,甲竞争力<乙,竞争强度弱→强→弱

B:t2—t3内甲种群出生率下降,死亡率上升,但出生率仍大于死亡率

C:t1—t2内甲、乙种群呈“S”增长

D:t3—t5内甲、乙两种群的年龄组成不同

上一题 下一题 0.0难度 选择题 更新时间:2018-09-24 04:31:35

答案(点此获取答案解析)

C

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阅读理解

    It's a white Christmas in the United States today, with snow falling from Seattle to Maine.

    Northeast

    Biting winds with snow swept the Northeast.

    Earlier, up to 15 inches of snow fell during a snow storm in Maine, while up to one foot fell in New Hampshire. Winds reached 76 mph on Cape Cod, Massachusetts, while up to 61 mph winds tore through Long Island, New York. Falling snow collected on the runways at Boston's Logan International Airport, causing temporary flight delays.

    The wind was so severe in Pennsylvania and New Jersey that the annual (重演) of George Washington and his soldiers'crossing the Delaware River was canceled, the Washington Crossing Historic Park told ABC News.

    Midwest

    Heavy lake effect snow fell in western Michigan.

    The National Weather Service has issued a wind-chill warning and advisory (公告) from Montana to Michigan. Bitter cold air in the Midwest produced wind chills Monday morning as low as minus 48 degrees in North Dakota and minus 47 in northern Minnesota.

    As this bitter cold made its way east overnight, it was expected to move over relatively mild Great Lakes, producing intense lake-effect snow bands capabie of producing 2 to 4 inches of snow in an hour.

    West Coast

    That storm system moved overnight through the Rockies, bringing more snow and the threat of avalanches(雪崩). The National Weather Service has issued an avalanche warning for the Wasatch Range Mountains outside Salt Lake City.