新概念3第一课puma at a large课后的多项选择题中的结构题（新版的是17页）___________________it immediately ran away.a) Observing her b)On being observedc)Having been observed d) On her being observed选什么呢 原因?
问题描述：
新概念3第一课puma at a large
课后的多项选择题中的结构题（新版的是17页）
___________________it immediately ran away.
a) Observing her b)On being observed
c)Having been observed d) On her being observed
选什么呢 原因?
答
选b
意思是一被发现,它就逃跑了
主句也就是it immediately ran away 的主语是it 也就是那个puma ,从句如果要省略主语的话,从句的主语也必须是puma.所以原句应该是
On it was boserved ,it immidiately ran away.而 一...就...的结构选bd,所以只能选b