A newspaper writer will write an article about the mean age of voters. She will estimate by selecting a sample of voters and calculating their mean age.

Which method should the writer use to select the sample?

A. select 100 people who voted for the most popular candidate in the last election

B. randomly select 100 people who voted in the last election

C. randomly select 100 people who read the newspaper

D. select 100 people who voted in the last election and are more than 39 years old