急问几道语法，请帮忙解答

A.     chores; by 1997 they had spent nearly six hours a week

B.    chores; by 1997 that figure had grown to nearly six hours a week

C.     chores, whereas nearly six hours a week were spent in 1997

D.    chores, compared with a figure of nearly six hours a week in 1997

E.     chores, that figure growing to nearly six hours a week in 1997

本题为什么不选A？

2.

The steel industry has changed radically over the last two decades, as large, integrated companies such as Bethlehem Steel once conducted operations from mining at one end of the process to shipping at the other have greatly downsized, or in some cases shut down altogether.

A.                 as large, integrated companies such as Bethlehem Steel

B.                as large, integrated companies, such as Bethlehem Steel, that
       

C.                 with large, integrated companies, such as Bethlehem Steel, that

D.                while large, integrated companies, such as Bethlehem Steel, that

E.                 and large, integrated companies such as Bethlehem Steel

为什么选B而不选A

3. Sound can travel through water for enormous distances, prevented from dissipating its acoustic energy as a result of boundaries in the ocean created by water layers of different temperatures and densities.
A. prevented from dissipating its acoustic energy as a result of
       
B. prevented from having its acoustic energy dissipated by
C. its acoustic energy prevented from dissipating by
D. its acoustic energy prevented from being dissipated as a result of
       
E. preventing its acoustic energy from dissipating by
       
                            

为什么选C

请好心人麻烦详细解释一下把，马上考了，急，谢谢

The steel industry has changed radically over the last two decades, as large, integrated companies such as Bethlehem Steel once conducted operations from mining at one end of the process to shipping at the other have greatly downsized, or in some cases shut down altogether.

A.                 as large, integrated companies such as Bethlehem Steel

B.                as large, integrated companies, such as Bethlehem Steel, that
       

C.                 with large, integrated companies, such as Bethlehem Steel, that

D.                while large, integrated companies, such as Bethlehem Steel, that

E.                 and large, integrated companies such as Bethlehem Steel

为什么选B而不选A

3. Sound can travel through water for enormous distances, prevented from dissipating its acoustic energy as a result of boundaries in the ocean created by water layers of different temperatures and densities.
A. prevented from dissipating its acoustic energy as a result of
       
B. prevented from having its acoustic energy dissipated by
C. its acoustic energy prevented from dissipating by
D. its acoustic energy prevented from being dissipated as a result of
       
E. preventing its acoustic energy from dissipating by
       
                

为什么选C

请好心人麻烦详细解释一下把，马上考了，急，谢谢