A statistics student considered many methods for collecting data from adults to estimate support for lowering the voting age to 16 years old. Which of the following methods would be least likely to include sampling bias?
a random sample of 500 adults in the state
a random sample of 200 students at a large high school
a survey of people leaving the local mall on the weekend
an online survey where adults are invited to share their opinions

I need the right answer to this ASAP