At a large conference of teachers from a variety of subjects, a random sample of 50 mathematics teachers attending the conference was selected. Among the selected mathematics teachers, 28 percent had taken one or more courses in statistics. For which of the following populations is 28 percent a reasonable estimate of the percentage of those who have taken one or more courses in statistics? 
选项为:A:All mathematics teachers  B:All mathematics teachers who attended the conference  C:All mathematics teachers who have taken one or more courses in statistics  D:All teachers who attended the conference  E:All teachers  请回答其中一个选项.