美国研究生入学考试难句解读-5（在线收听） |
| The isotopic composition of (65) lead often varies from one source of common copper ore to another, with variations exceeding the measurement error; and preliminary studies indicate virtually uniform is topic composition (70) of the lead from a single copper-ore source. 铅的同位素构成经常在一种普通铜矿石来源与另一种铜矿石来源之间存在差异，其差异程度超出测量误差；而最初的研究表明，对于来自单独一个铜矿石来源的铅来说，其同位素构成几乎是毫无二致的。 More probable is bird transport, either externally, by accidental attachment of (20) the seeds to feathers, or internally, by the swallowing of fruit and subsequent excretion of the seeds. 更有可能的是鸟类运输：或者是通过外部途径，即由于种籽偶然粘附在羽毛上；或者是通过内部方式，即由于鸟类吞食果子并随后将种籽排泄出来。 It is not known how rare this resemblance is, or whether it is most often seen in inclusions of silicates such as garnet, (25) whose crystallography is generally somewhat similar to that of diamond; but when present, the resemblance is regarded as compelling evidence that the diamonds and inclusions are truly (30) cogenetic. 现在尚不知这种类似稀少到何种地步，也不知道是否它最常见于象石榴石一类的硅酸盐内含物中，而这类物质的晶体结构普遍地在 某种程度上类似于金刚石的晶体结构。但一旦存在，这种类似就被视作极有说服力的证据，证明金刚石与内含物确是同源的。 |
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