chest可以指胸腔或柜子、箱子，medicine chest是“药箱”的意思。

　　potential在句中用作名词，意思是“潜力”，potential也可用作形容词，意思是“潜在的”。

　　1)they are determined to tap their potential to the full. (他们决心充分挖掘自己的潜力。)

　　2)the aim of this advertisement is to attract potential customers. (这则广告的目标是吸引潜在的顾客。)

　　3)you have to know more about the potential demand of the market。(你得对市场上可能达到的需求量有更多的了解。)

　　5.in today`s pharmaceutical market 15 of the 125 drugs derived from plants were discovered in the rainforest. derived from plants是现在分词短语做定语，相当于被动语态的定语从句。如：

　　1)the beer bought from the supermarket is very light. (在超市买的那啤酒口味很淡。)

　　2)the candy made from cactus tastes strange. (用仙人掌做的糖果味道很怪。)

　　15 of the 125意思是125中的15。再如two of the three (三个中的两个)

　　derive from意思是get from， obtain from， 如：

　　1)much of his knowledge is derived from books. (他的许多知识得自书本。)

　　2)he derived his stories from his experiences in the countryside. (他的故事来自于他在农村的经历。)

　　6.rare birds and animals that cannot be found anywhere else in the world have been disappearing at the rate of one a year since the turn of the century。

　　句中的else是形容词，常接在不定代词的后面，表示“其他的，别的”，如：

　　1)is there anything else i can do for you?(我还能为你做些别的事吗?)

　　2)did anybody else know this? (有其他人知道这件事吗?)

　　3)he didn`t go anywhere else. (他没去其他地方。)

　　one a year意思是“每年一种”。这种表达方式在英语中很常用，如：

　　1)take the medicine three times a day. (每日三次服这种药。)

　　2)they met three times a week. (他们每周见三次。)

　　3)he finishes 5 books a month. (他一个月读完五本书。)

　　当时间状语用since引导时，句子中的时态常用完成时。如：

　　1)he has been living here since he came to nanjing 5 years ago. (自从他五年前来到南京，他就一直住在这儿。)