难句类型：复杂修饰、插入语、倒装
more probable is bird transport，either externally，by accidental attachment of the seeds to feathers，or internally，by the swallowing of fruit and subsequent excretion of the seeds. （3+）
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。
解释：句首有一个倒装，正常语序是bird transport is more probable。后面的句子中由于插入部分的频繁出现使句子显得十分凌乱。
训练：more probable is bird transport，either externally，by accidental attachment of the seeds to feathers，or internally，by the swallowing of fruit and subsequent excretion of the seeds.