請看這道題，這個until 后要接過去分詞嗎?
He is a man of few words, and seldom speaks until _________ to.
A. spoken B. speaking C. speak D. be spoken
【分析】此題容易誤B，認為until 是介詞，后接動詞時用動名詞形式。其實，此題應選A，until spoken to 為 until he is spoken to 之省略。句意為“他是個沉默寡言的人，別人不同他說話，他很少同別人說話”。按英語習慣，一些表示時間、地點、條件、方式、 讓步等的狀語從句，若其主語與主句主語一致，且從句謂語包含動詞be, 那么可將從句的主語和動詞be省略：
You must study hard while (you are) young, or you will regret when (you are) old. 趁年輕時要努力學習，不然到老了你會后悔的。
I won't go unless (I am) invited. 我不會去, 除非請我。
Look out for cars when (you are) crossing the streets. 過馬路時要注意汽車。
While (I was) waiting I was reading some old magazines. 等的時候我在看一些舊雜志。
He worked very hard though (he was) still rather poor in health. 盡管身體還不好，但他仍努力工作。
He will work hard wherever (he is) sent by the Party. 無論黨把他派往哪里,他都會努力工作。
請再看兩道試題：
(1) If carefully _________, the experiment will be successful.
A. do B. does C. done D. doing
答案選C，可視為 if it is carefully done 之省略。
(2) The research is so designed that once _________ nothing can be done to change it.
A. begins B. having begun C. beginning D. begun
答案選D，可視為 once it is begun 之省略。
