Although these molecules allow radiation at visible wavelengths, where most of the energy of sunlight is concentrated, to pass through, they absorb some of the longer-wavelength, infrared emissions radiated from the Earth’s surface, radiation that would otherwise be transmitted back into space.
1. 句首的“although”引导让步状语从句,于是“these molecules”属于这个从句。“allow radiation”形成动宾关系,且跟前面的“these molecules”紧邻,那么这三者形成了一个完整的主谓宾结构;
2. “visible wavelengths”被“at”间隔紧随“radiation”后,形成“名词+介词+名词”结构。这种结构中,介词+后面的名词做前名词的后置定语;
3. “where most of the energy of sunlight is concentrated” 在句中做定语从句,修饰离它最近的名词(一般情况下定语从句修饰离它最近的名词,但反例也很多,我们可借助句意辅助判断)“visible wavelengths”;
4. 把上面的定语,定语从句忽略掉,可以看出“although”后面简化后即“these molecules allow radiation to pass through”。不定式“to pass through”在这个让步状语从句中做小一级别的目的状语。
5. 让步状语从句之后,“they absorb”明显成为主语的主谓,其中“they”指代复数名词“molecules”;
6. “absorb”的宾语相对隐蔽。仔细看我们会发现“radiated from the Earth’s surface”为典型的过去分词短语做名词“emissions”后置定语;而前面的“the longer-wavelength, infrared”则做“emissions”的前置定语。这时可以看出“emissions”是主句宾语;
7. 最后一个逗号后的名词“radiation”后紧跟了以“that”为标志的后置定语从句,于是我们可以把它看成词组。进一步细查otherwise我们会看到这些“radiation”就是前面出现的“emissions”, 它或者“be absorbed by ‘these molecules’ ”或者“be transmitted back into space”。于是 “radiation”一直到结尾做“emissions”的同位语。