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下图是现在家养的鸡的品种，种类很多，但是它们的祖先却是同一种野生鸡---原鸡。试运用生物进化的观点解释其形成过程。 (1)从图中可以看出不同品种的鸡有共同的________。 但在不同的饲养条件下，原鸡产生了许多_________， 其中有些产蛋多些，有些长肉多些，而且这些变异都是_________（可遗传、不可遗传）的。 (2)人们根据各自的爱好，对不同变异的鸡进行________，如有的人需要产蛋多的鸡，就杀死了产蛋少的鸡，留下产蛋多的鸡用来繁殖后代，这样逐代下去，“产蛋多”这种______就会逐代积累而得到加强，就培育出产蛋多的鸡，如北京白鸡。 (3)上述事实说明，鸡的变异方向是________的，而选择是________的。
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【简答题】Nancy’s hobby is collecting sharpeners. She spends a lot of time on it after school. She has been collecting more than one hundred sharpeners from different countries. They are all different in color ...
【单选题】The effect of free surface on initial stability depends upon（）.
A.
the amount of liquid in the compartment
B.
the dimensions of the liquid surface and the vessel's displacement
C.
only the length of the compartment
D.
the vertical position of the liquid in the vessel
【单选题】When the government spends more, the initial effect is that
A.
aggregate demand shifts right.
B.
aggregate demand shifts left,
C.
aggregate supply shifts right
D.
aggregate supply shifts left
【单选题】Other things the same, when the government spends more, the initial effect is that ( )
A.
aggregate demand shifts right.
B.
aggregate demand shifts left.
C.
aggregate supply shifts right.
D.
aggregate supply shifts left.
【单选题】A severe drought has damaged this year's lettuce crop. The initial effect on the lettuce market is a
A.
decrease in the demand for lettuce.
B.
decrease in the supply of lettuce.
C.
decrease in both the demand and supply of lettuce.
D.
rightward movement along the demand curve for lettuce.
【单选题】The initial effect of an increase in the money supply is to
A.
increase the interest rate.
B.
increase the price level.
C.
decrease the price level.
D.
decrease the interest rate.
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