英語長難句是包含各種語法關(guān)系和特殊句型的句子。長難句中可能含有多個從句，從句和從句之間還有多種多樣關(guān)系。而在GRE閱讀中這種性質(zhì)的句子數(shù)不勝數(shù)，這是因為英語可以有后置定語，擴展的后置定語可以是帶從句或長修飾語的復(fù)雜句，這些句子結(jié)構(gòu)復(fù)雜，邏輯性強，很容易就能讓考生陷入絕望當(dāng)中。但是，無論多長的句子還是復(fù)雜的結(jié)構(gòu)，它們都是由一些基本的語法成分組成的，因此只要弄清原文的句法結(jié)構(gòu)，找出整個句子的中心內(nèi)容及其各層意思，然后分析各層意思之間的邏輯關(guān)系，最后就能把這些句子攻克?，F(xiàn)在，我們拿GRE閱讀的一篇文章為例。
原文：
Geologists have long known that the Earth's mantle is heterogeneous, but its spatial arrangement remains unresolved—is the mantle essentially layered or irregularly heterogeneous? The best evidence for the layered-mantle thesis is the well-established fact that volcanic rocks found on oceanic islands, islands believed to result from mantle plumes arising from the lower mantle, are composed of material fundamentally different from that of the mid ocean ridge system, whose source, most geologists contend, is the upper mantle. Some geologists, however, on the basis of observations concerning mantle xenoliths, argue that the mantle is not layered, but that heterogeneity is created by fluids rich in "incompatible elements" (elements tending toward liquid rather than solid state) percolating upward and transforming portions of the upper mantle irregularly, according to the vagaries of the fluids' pathways. We believe, perhaps unimaginatively, that this debate can be resolved through further study, and that the underexplored mid ocean ridge system is the key.
難句：
The best evidence for the layered-mantle thesis is the well-established fact that volcanic rocks found on oceanic islands，islands believed to result from mantle plumes arising from the lower mantle，are composed of material fundamentally different from that of the mid-ocean ridge system， whose source，most geologists contend，is the upper mantle.
這個句子的難點主要在于復(fù)雜的修飾和插入語。本句前面的主干并不算難，即the evidence is the fact that。難就難在fact之后說明fact 的同位語從句。此從句中既有大段插入語，又有從句，較為難讀。同位語從句的主語是volcanic rocks，主語后面的found on oceanic islands是分詞修飾volcanic rocks的；islands后面又有一個說明islands的同位語islands believed to result from mantle plumes arising from the lower mantle，此同位語實際起到一個分隔主謂的同位語的作用。其后是謂語動詞are composed/of fundamentally different from that of the mid ocean ridge system, whose source, most geologists contend, is the upper mantle。
Some geologists，however，on the basis of observations concerning mantle xenoliths， argue that the mantle is not layered，but that heterogeneity is created by fluids rich in "incompatible elements" (elements tending toward liquid rather than solid state) percolating upward and transforming portions of the upper mantle irregularly，according to the vagaries of the fluids’ pathways.
這個句子難點同樣是復(fù)雜修飾和插入語。本句的主句中有一個長插入語however, on the basis of observations concerning mantle xenoliths, 割裂了主謂，但句子的主要難度還是在that引導(dǎo)的賓語從句中，從句中有由but 所連接的兩個句子，一起延續(xù)到句末。首選是rich in incompatible elements修飾fluids；后面又有一個同位語和一個分詞結(jié)構(gòu)，都是修飾incompatible elements的，最后還有一個狀語來修飾那個分詞結(jié)構(gòu)，層層修飾，比較復(fù)雜。
原文：
Geologists have long known that the Earth's mantle is heterogeneous, but its spatial arrangement remains unresolved—is the mantle essentially layered or irregularly heterogeneous? The best evidence for the layered-mantle thesis is the well-established fact that volcanic rocks found on oceanic islands, islands believed to result from mantle plumes arising from the lower mantle, are composed of material fundamentally different from that of the mid ocean ridge system, whose source, most geologists contend, is the upper mantle. Some geologists, however, on the basis of observations concerning mantle xenoliths, argue that the mantle is not layered, but that heterogeneity is created by fluids rich in "incompatible elements" (elements tending toward liquid rather than solid state) percolating upward and transforming portions of the upper mantle irregularly, according to the vagaries of the fluids' pathways. We believe, perhaps unimaginatively, that this debate can be resolved through further study, and that the underexplored mid ocean ridge system is the key.
難句：
The best evidence for the layered-mantle thesis is the well-established fact that volcanic rocks found on oceanic islands，islands believed to result from mantle plumes arising from the lower mantle，are composed of material fundamentally different from that of the mid-ocean ridge system， whose source，most geologists contend，is the upper mantle.
這個句子的難點主要在于復(fù)雜的修飾和插入語。本句前面的主干并不算難，即the evidence is the fact that。難就難在fact之后說明fact 的同位語從句。此從句中既有大段插入語，又有從句，較為難讀。同位語從句的主語是volcanic rocks，主語后面的found on oceanic islands是分詞修飾volcanic rocks的；islands后面又有一個說明islands的同位語islands believed to result from mantle plumes arising from the lower mantle，此同位語實際起到一個分隔主謂的同位語的作用。其后是謂語動詞are composed/of fundamentally different from that of the mid ocean ridge system, whose source, most geologists contend, is the upper mantle。
Some geologists，however，on the basis of observations concerning mantle xenoliths， argue that the mantle is not layered，but that heterogeneity is created by fluids rich in "incompatible elements" (elements tending toward liquid rather than solid state) percolating upward and transforming portions of the upper mantle irregularly，according to the vagaries of the fluids’ pathways.
這個句子難點同樣是復(fù)雜修飾和插入語。本句的主句中有一個長插入語however, on the basis of observations concerning mantle xenoliths, 割裂了主謂，但句子的主要難度還是在that引導(dǎo)的賓語從句中，從句中有由but 所連接的兩個句子，一起延續(xù)到句末。首選是rich in incompatible elements修飾fluids；后面又有一個同位語和一個分詞結(jié)構(gòu)，都是修飾incompatible elements的，最后還有一個狀語來修飾那個分詞結(jié)構(gòu)，層層修飾，比較復(fù)雜。