一、状语从句中句子成分的省略
在以when, while, if, as if, though (although), as, whether, once等连词引导的时间、原因、条件、方式、让步等状语从句中，常常省略相同的主语或作主语的代词it以及be动词,保留现在分词、过去分词、介词短语、不定式等。
e.g. 1. Generally speaking, ________according to directions, the drug has no side effect.
A. when taking B. when taken
C. when to take D. when to be taken
2. Though ________ money, his parents managed to send him to university.
A. lacked B. lacking of C. lacking D. lacked in
3. When ________, the museum will be open to the public next year.
A. completed B. completing C. being completed D. to be completed
