在科学写作中，下列哪个句子是正确的?

1. Most of the respondents were students. Which is understandable because the posters calling for volunteers were displayed mainly at our university.

2. The interviewees, of which most were postgraduates, were first asked to complete a questionnaire.

3. All questionnaires, through which we went twice, were complete and were included in this study.

4. The questionnaire answers provided useful information on strategies of coping with different types of stress, which are summarized below.

这些句子包含使用关系代词“which”的定语从句，用来指代前面提到的事物，但是在正式的科学写作中这四个句子都是错误的。

在句子（1）中，以“which”开头的是一个非限定性定语从句，指代的是前面的整个句子。然而，以关系代词开头的句子是非正式的。正式的写法是“Most of the respondents were students, which is understandable because the posters calling for volunteers were displayed mainly at our university.”

句子（2）使用非限定性定语从句来补充关于“interviewees”的信息。然而，因为在介词后面，需要使用人称关系代词的宾语形式（“whom”）。此外，在这个句子中，“most of whom”听起来更自然，即“The interviewees, most of whom were postgraduates,…”。

句子（3）也包含一个非限定性定语从句，但是动词短语“to go through”（意思是examine）有一个不可分割的介词。因此，“went through”应该放在一起，从句应该是“which we went through twice”。但是，“to go through”听起来不正式，所以这个从句最好改为"which we reviewed twice"。

在句子（4）中，“which”指的是答案、信息、策略、各种类型的压力，还是指前面的整个分句，这一点并不清楚。最好用一个新句子来表达清楚（例如，“The most commonly cited strategies are summarized below”）。