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1
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2
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(1)??
(2)??
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a?ß
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??ABC ???DBC
(3)??
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3
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4
2.????
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??AB?a,AB?CD
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?AB?BE?
????aCD ß?????,?a?ß?
5
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6
?1??????P-ABC?,ABAC,PA??? ABC,D?BC??,????PAD???PB
C
P
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?ABAC ,BDDC ?BC?AD
A
?BC?PA
B
D
C
?BC???PAD
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7
3.????
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??AB ? ß?
?????ß???B?BE?CD, ??ABE????a-CD-ß????
?a?ß,??AB?BE
?AB?ß
??AB?CD,
8
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9
?2???????????????????????,???????????????
10
4???
(1)?????????????
(2)?????????
(3)?????????
11
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??ABCD????,SD???AC, ??????7????,????????????
1.??SAD???ABCD 2.??SBD???ABCD 3.??SCD???ABCD 4.??S
AD???SCD 5.??SBC???SCD 6.??SAB???SAD 7.??SAC???SBD
12
???? ??9.7?5?6