Many scientists are sure will be useless learning a theory without practice．A.thatB.that itC.it thatD.there 题目和参考答案——青夏教育精英家教网—

     A Low-Carbon Economy (LCE) refers to an economy which has a minimal emission of greenhouse gas
(GHG), namely, carbon dioxide into the biosphere (生物圈). Recently, most of the scienti sts and the public
hold the opinion that the climate is changing because there is such an accumulation of CO2 in the atmosphere
due to human activities. The over-concentration of these gases is producing global warming that affects
long-term climate, with negative impacts on humanity in the foreseeable future. LCE, therefore, is proposed
as a means to avoid catastrophic climate change.
     All nations which are considered carbon intensive societies and societies which are heavily populated
should become zero-carbon societies and economies. Several of these countries have promised to become
'low carbon' but not entirely zero carbon, and claim that emissions will be cut by 100% by balancing emissions
rather than ceasing all emissions.
     Nuclear power and the strategies of carbon capture and storage (CCS) have been proposed as the primary
means to achieve a LCE while continuing to exploit non-renewable resources. Scientists are afraid, however,
whether the spent-nuclear-fuel can be stored, and whether it is secure. Also they are not certain about the
costs and time needed to successfully implement CCS worldwide and whether the stored emissions will leak
into the biosphere or not. Alternatively, many have proposed renewable energy should be the main basis of a
LCE, but, they have their associated problems of high-cost and inefficiency; this is changing, however, since
investment and production have been growing significantly in recent times. Furthermore, it has been proposed
that to make the transition to an LCE economically attractive we would have to attach a cost (per unit output)
to GHGs through means such as emissions trading and/or a carbon tax .
     A LCE is aimed to integrate all aspects of itself from its manufacturing, agriculture, transportation to
power-generation around technologies that produce energy and materials with little GHG emission and thus
around populations, buildings, machines and devices which use those energies and materials efficiently and
dispose of or recycle its wastes so as to have a minimal output of GHGs.

Title:   1
I.   2 : an economy with a minimal output of GHG
II.   3 of the present economy:
     ● global warming
     ● long-term climate change
     ●   4 on humanity
III.   5 :
     ● to produce energy and materials with little GHG emission
     ● to use those energies and materials efficiently
     ● to have   6 of GHGs
IV.   7 to achieve a LCE:
      ● nuclear power
      ● the strategies of carbon capture and storage
     ● renewable energy
     ●   8
     ● a carbon tax
V.   9 :
     ● spent-nuclear-fuel storage / storage of spent-nuclear-fuel
     ●   10
     ● uncertainty about the costs and time needed

Many scientists are sure ________will be useless learning a theory without practice．

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