Answer: c) Ethnic background.
Explanation:
Persuasive speech is used for helping the audience to understand , explain and educate about a certain topic so that they be aware and work in certain direction according to their point-of-view.
According to the question, while giving persuasive speech on immigration reform , the audience is being informed about improving legal migration and eliminating any sort of illegal migration. People's ethnic background should be considered as immigration involves country ,culture, religion etc and according to audience ethics speech should be given.
Other option are incorrect because gender , measurement , sexual position and education are not the part related with immigration reform .Thus, the correct option is option(c).