这题，虽然看了解释，还是不明白，求高人赐教

zhangchuqi

                                                                                                                                                [size=10.000000pt]23. The Iroquois were primarily planters, but supplementingtheir cultivation of maize, squash, and beans withfishing and hunting.
                                       

                                               
•                                                         [size=10.000000pt](A)  but supplementing
  
                                                 
•                                                         [size=10.000000pt](B)  and had supplemented
  
                                                 
•                                                         [size=10.000000pt](C)  and even though they supplemented
  
                                                 
•                                                         [size=10.000000pt](D)  although they supplemented
  
                                                 
•                                                         [size=10.000000pt](E)  but with supplementing
  
                                         

                                        [size=10.000000pt]Grammatical construction; Verb form
                                        [size=11.000000pt]Th[size=11.000000pt]e participle [size=11.000000pt]supplementing [size=11.000000pt]would normally beexpected to modify the first clause, describing orextending its meaning, but the logic of thissentence demands a contrast, not an extension.Consequently, the second part of the sentencemust be revised to emphasize the contrastproperly. [size=11.000000pt]Th[size=11.000000pt]e logic of the sentence also arguesagainst a construction that would set the twoclauses and the importance of their content equalwhen they clearly should not be. [size=11.000000pt]Th[size=11.000000pt]e bestsolution is to have the main clause describe theprimary activity, and a subordinate clause,[size=11.000000pt]although they supplemented[size=11.000000pt], describe thesupplementary activity.
                                       

                                               
•                                                         [size=11.000000pt]A  [size=11.000000pt]Th[size=11.000000pt]e construction using [size=11.000000pt]supplementing[size=11.000000pt]fails to support the intended meaning ofthe sentence.
  
                                                 
•                                                         [size=11.000000pt]B  [size=11.000000pt]And [size=11.000000pt]does not convey contrast; [size=11.000000pt]hadsupplemented [size=11.000000pt]is the past perfect tense butthe simple past is required to match [size=11.000000pt]were.
  
                                                 
•                                                         [size=11.000000pt]C  [size=11.000000pt]And [size=11.000000pt]does not convey contrast and should beomitted; [size=11.000000pt]and even though [size=11.000000pt]creates a sentencefragment.
  
                                                 
•                                                         [size=11.000000pt]D  Correct. [size=11.000000pt]Using [size=11.000000pt]although [size=11.000000pt]creates a subordinateclause in this sentence and logically links thatclause with the main clause; the simple past[size=11.000000pt]supplemented [size=11.000000pt]parallels the simple past [size=11.000000pt]were[size=11.000000pt].
  
                                                 
•                                                         [size=11.000000pt]E  [size=11.000000pt]But with [size=11.000000pt]is awkward and unclear;[size=11.000000pt]supplementing [size=11.000000pt]is a modifier when acontrasting clause is needed.