例句：
Certain of those present were unwilling to discuss the matter further.
某些在场的'人不愿意进一步讨论这个问题。
Those beliefs still prevail among certain social groups.
这些信念在某些社会群体中仍很盛行。
The work must be completed within a certain time limit.
这项工作必须在一定期限内完成。
The company's financial position is not certain.
这家公司的财务状况不明朗。
Many animals breed only at certain times of the year.
很多动物只在一年的某个时候繁殖。