我做题的时候也考虑了究竟是单纯吸收还是兼有释放的问题。最终排除了单纯吸收。理由有2: 1。Agronomists studying the herb have discovered that it produces large amounts of histidine. 请注意用词:produces; 2。即使1没有说服力,herb只是单纯吸收,E也不对。因为不论成熟与否,herb每天都会吸收新的有害金属。现在要证明的是histidine对抵抗有害金属起作用,用"E成熟后分泌的histidine减少"不足以作为理由。至少也应该是“成熟后没有减少“才对。
In D, the herbs can make the soils suitable for other plants, there are two possibilities, 1)the herbs release the histidine to soil to inert metal,--the reaction happens in the soil 2)the herbs absorb all the metals from soil,--the reaction happens in the bodies of herbs. since the metals are high concertrated in the soil, (1)can not be true because the herbs should be hurted before they release histidine.
Since the chemical reaction happens in the bodies of herbs, not in the soil, it is also possile that the herbs use materials other than histidine to protect themselves after they absord the metals.
C说:others of the closely related group of plants are also found to produce histidine in large quantities,herb是属于这个group没错,而这个group也是能thrive in soil with high concentrations of metals,问题是C并没有指出其他能产生大量histidine的植物是在高铁环境生存时产生这些histidine啊,有可能它们在任何环境下都会产生这些histidine呢?如果是这样的话就变成削弱啦!