在例3中，我们要讨论的问题为第二句中由when引导的两个从句。从语法结构来看，原译的when是作为关系副词来用的，用when引导的两个并列定语从句修饰present。但英语中 at present已成为固定搭配，意思为now,是副词性质。这样由 when引导的定语从句就没有了先行词。若将when从句视为时间状语从句，显然也是不通的。从语义上来看，例3的第一句为陈述一种事实或观点，而This is especially true为一个结论，由 when引导的两个从句的内容则应该是该结论的论据，即为表示原因的成分。因此，无论从语法上看，还是从语义上讲，用关系副词 when引导定语从句均是不适宜的。

 

改译：The diversity of the domestic animals in China is not only valuablse for providing resources for animal breeding, but also an imporiant component of the treasure of animal genetic resources both of China and of the world. This is especially important, for the biological diversity of the domestic animals in other countries is becoming more and more depleted, and for ihe domestic animal resources are decreasing and becoming more and more homogeneous.