在数学中，如果一个方程组有唯一解，那么下列哪个条件必须满足？

A researcher conducts a survey to understand public opinion on a newly implemented policy. The survey results indicate that 70% of respondents support the policy. However, the researcher later discovers that the survey was primarily distributed through an online platform that is mainly used by a specific demographic group that is known to be more likely to support the policy. What is the most significant limitation of this survey's findings?

若向量组α1, α2, ..., αm的秩为m，以下哪个结论是正确的？

在夜间行驶时，何时应该使用远光灯？

自媒体选择不导流的主要原因是什么？