急急!!中文轉英文>>”受訪者是中學生，而他們的回覆率很高”

The interviewees are secondary school students , and their percentage of feedback is very high.

"受訪者是中學生，而他們的回覆率很高"
The interviewers (mostly) are high school students, their feedback percentage is pretty high.
Very likely, the word "interviewer" is the right word as '受訪者' and not "participant" (關係者;參與者) 資料 from: English Heritage

The participants of the interview are secondary school students, and their response rate is high.

you can choose to use present tense or past tense here, but I would recommend present tense.
Although it is a past event, it is still true that the participants are secondary school students, and the response rate is high.

The participants were mostly secondary school students and their response rate was high.

〝受訪者是中學生，而他們的回覆率很高〞 轉成英文是 : The participant are middle-school studentands and their reply rate is enough

2009-06-16 23:24:35 補充：
The participant are middle-school students and their reply rate is enough

2009-06-18 14:12:57 補充：
The participants are secondary school students and their reply rate is enough