Knowledge on symptoms and signs of dengue fever (DF).

All P-values are based on chi-square analysis of numbers in highland and lowland categories except those indicated by an asterisk (*) which are based on Fisher's exact test. Responses in bold font indicate correct answer.所有P值均基于对高地与低地类别数据的卡方检验（chi-square analysis）计算所得，带星号（*）标注的P值除外，此类P值采用费希尔精确检验（Fisher's exact test）计算。以加粗字体呈现的作答为正确答案。