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八、同位语结构
同位语考试形式一 ：名词作主语，主语同位语 ___, __ _, ___ (注意是两个逗号)
例1：The tongue , ___, is an important aid in chewing and swallowing .
(A) is the chief organ of taste (B) tasting the organ chiefly
(C) the chief organ of taste (D) the organ chiefly tastes
分析：空格处显然缺定语或同位语。句中已有谓语动词is, 故先排除A和D。(B)不合题意，故也可排除。(C)是名词短语，适合作主语的同位语，使句子完整，句意正确，故选(C)。
同位语考试形式二 ：名词作主语，后面的名词是主语同位语，解释说明后面的名词
___, ___ (注意是一个逗号)
例2：A prolific writer of prose and verse, ___of Native Americans in her novel, Century of Dishonor.
(A) Helen Hunt Jackson took up the cause (B) the cause taken up by Helen Hunt Jackson
(C) was Helen Hunt Jackson's cause (D) the cause that Helen Hunt Jackson took up.
分析：空格前为名词短语，空格后为介词短语，空格处明显缺主语和谓语动词。根据空格前名词短语的意思判断，主语应该是人名而不是指物的名词，故选(A)。
例3：Often very annoying weeds ,___and act as hosts to many insect pests.
(A) that crowd out less hardy plants than goldenrods (B) crowding out less hardy plants by goldenrods (C) the goldenrod's crowding out of less hardy plants (D) goldenrods crowd out less hardy plants
分析：空格后面是and, 句中缺少与and并列的谓语动词。A只有从句没有主句; B,C分别是分词和名词短语, 无法与动词act并列; D 包含主语的同位语goldenrods和谓语动词crowd，故选(D)
同位语考试形式三 ：主谓宾后面出现一个名词，那么名词可以作宾语或者表语的同位语
例4：An Olympic marathon is 26 miles and 385 yards, approximately___from Marathon to Athens.
(A) the distance is (B) that the distance is (C) is that the distance (D) the distance
分析：逗号前为完整的句子，后面如果再接句子一定要有连接词或者从句引导词。A、B、C均为主谓结构，但都没有从句引导词，故排除。D是名词短语作表语同位语，故选(D)。