国外越来越多的科研人员喜欢在论文中使用主动语态。他们认为被动语态句子通常使用更多的单词，可能表达含糊不清，并可能导致介词短语的混乱。
论文写作要求虽然严格，但并未强制规定语态方式，大家可灵活运用，但了解二者的不同还是很重要的。
在以主动语态写成的句子中，句子的主体执行动作。在用被动语态写的句子中，主体接受动作。
Active: The candidate believes that Congress must place a ceiling on the budget.
Passive: It is believed by the candidate that a ceiling must be placed on the budget by Congress.
Active: Researchers earlier showed that high stress can cause heart attacks.
Passive: It was earlier demonstrated that heart attacks can be caused by high stress.
Active: The dog bit the man.
Passive: The man was bitten by the dog.
何时使用被动语态？
强调动作而不是行动者：After long debate, the proposal was endorsed by the long-range planning committee.
2. 在整个段落中保持主题和焦点一致
The data processing department recently presented what proved to be a controversial proposal to expand its staff. After long debate, the proposal was endorsed by . . . .
3. 不指名道姓以使行文流畅
The procedures were somehow misinterpreted.
4. 描述行为者未知的或不重要的情况
Every year, thousands of people are diagnosed as having cancer.
5. 命令式的语气
Visitors are not allowed after 9:00 p.m.
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