33.It is　one of nature's great ironies that the　availability of nitrogen in the soil frequently sets an upper limit on plant growth even though the plants' leaves　are bathed in a sea of nitrogen gas.下述情形真可谓是自然界的一个莫大讽刺：土壤中所能获得的氮肥量往往对植物的生长构成了一个上限，虽然植物的叶子被沐浴在一片氮气的海洋中。

34.Unless they succeed，the　yield gains of the Green Revolution will be largely lost even if the genes in　legumes that equip those plants to enter　into a symbiosis with nitrogen fixers　are identified and isolated，and even if　the transfer of those gene complexes，once they are found， becomes possible.
除非他们能取得成功，不然的话，绿色革命的产量收益将在很大程度上损失殆尽，即使豆科植物中使这些植物有条件进入到与固氮细菌共生关系的基因可被辨识出来和分离开来的话，且即使这些基因综合体（gene complex），一旦被发现之后，其移植得以成为可能的话。

35.Its subject（to use Maynard Mack's categories）is　“life-as-spectacle，” for readers，diverted by its various incidents，observe its hero Odysseus primarily from without；the tragic Iliad，however，presents “life-as-experience”：readers　are asked to identify with the mind ofAchilles，whose motivations render him a not particularly likable hero.
其主题〔若借鉴梅纳德。迈克（Maynard Mack）的两个分类范畴的话〕是“人生作为外部景象”，因为读者的注意力被作品那形形色色的事件所分散，主要是从外部来观察其主人公奥德修斯（Odyssus）的；然而，富于悲剧色彩的《伊利亚特》所表现的则是“人生作为内心体验”：读者被要求与阿基琉斯（Achilles）的心灵产生共鸣，而其行为动机却致使他变作一个并非特别惹人喜爱的主人公。

36.Most striking among the many asymmetries evident in an adult flatfish is eye placement： before maturity one eye migrates，so that in an adult flatfish both eyes are on the same side of the head.
在一条成年比目鱼身上显著存在的诸多不对称（asymmetry）特征中，最为吸人注目的是眼睛的摆位：在成年之前，一只眼睛发生移动，因此在成年比目鱼身上，两只眼睛均位于头部的同一侧面。

37.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 midocean ridge system， whose source，most　geologists contend，is the upper mantle.
对于地幔分层论点来说，最好的证据乃这样一个确认的事实，即在那些海洋岛屿——这些岛屿据信是源于由下层地幔升上来的地幔柱状溶岩流（mantle plume）——上发现的火山岩石，是由与海洋中部山脊系统的物质根本不同的物质构成的，而这一海洋中部山脊系统的成因，大多数地质学家论辩道，为上部地幔。

38.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.
但是，某些地质学家，以对地幔捕虏岩体（xenolith）所作的观察为依据，指出地幔并非是分层排列的，相反，地幔的异质性是由那些富含“不相容成分”的流质构成的，这些成分趋向于流体而非固体的状态，自下而上渗透扩散，并依照这些流质流向的任意性，不规则地将上部地幔的某些部分予以改变。