過去分詞➕介詞
（1）過去分詞短語發生的動作在謂語動詞之前
（2）短語中的過去分詞與邏輯主語之間是被動關係
如：
I saw the ball thrown into the garden.
我看見球被扔進了花園。
過去分詞短語可以表達下列四種意思：
㈠方法或活動方式
如：
He walked up and down， lost in thought.
I sat before the desk until after mid-night， absorbed in writing.
Surrounded by a host of fans， the film star left the airport excitedly.
㈡原因，如：
Greatly disappointed， some staff decided to leave the place.
Taken by surprise， the enemy surrendered.
㈢時間，如：
Born and bred in a turbulent age， the older generation of people experienced all sorts of hardships.
Thrown to the floor， the boy regained his footing a few minutes later.
㈣條件
如：
Given more time， the slow learners would have done better.
Criticised by someone else， Tony would not have flared up like that.
除了直接修飾動詞之外，過去分詞或短語也可以和連詞合組成短語，表示下列意思：
⒈由 when， whenever， while， until 等連詞引導，表示“ 時間”
如：
When asked about his previous job， Bill said he had been a motor mechanic.
● Susan seldom speaks in class until spoken to.
⒉由 where， wherever 連詞引導，表示“地點”，如：
Mosquitoes should be completely exterminated where found.
Retirees in good health should be invited to return to work wherever needed.
⒊由 if， unless 引導，表示“條件”，如：
If kept for too long， some medicines will lose their effectiveness.
We have made a point of not attacking unless attacked.
