Lesson 1 A puma at large

spot (v) 看出，发现

oblige (v) 使...感到必须；obliged （adj）必须的， feel obliged to do sth. 感到不得不做某事 ==have to。eg：Experts felt obliged to investigate.

somehow (adv) 不知怎么搞地，不知什么原因

in the possession of, 为...所有

On being observed, it immediately ran away. 前面划线部分是分词短语，这时候分词短语的时态要看主语。

Pumas never attack a human being unless it is cornered.

Pumas never attack a human being except when they are concered.

unless 与 except后面加单独的句子成分，里面的成分不包含在主体之内。

could have done----could+动词完成时    表示：（1）过去曾有能力或有可能去做某件事，但未去做；（2）对过去行为的肯定推测

should have done 表示：（1）过去的动态本应发生而实际却未发生；（2）对过去动作发生的可能性推测

must be 和can only be   对现在行为的肯定推测

in a trap陷阱

intimately熟悉地