What is the correct article

Choose the correct answer. the phrase "por cierto" means: by certain for sure over there for now does anyone know the answer to this question?

Match each topic to the audience who would be most receptive to the topic. the audience is stay-at-home moms who are 30 to 40 years old. they are college-educated women who live in the suburbs. the audience is a group of male college students getting ready to graduate from college. they attend a large university in a big city. the audience is blue-collar workers who are 30 to 50 years old. they work in the steel industry in a small, rural community. the audience is retired men and women who are 70 to 80 years old. they live in a retirement community, and many of them have several grandchildren who live far away. the audience is a group of students getting ready to sign up for seventh-grade classes. they come from a wide range of intellectual levels, but many of the students travel extensively with their families. using a social networking website to connect with friends and family arrowright advantages of joining a labor union arrowright home schooling reform arrowright how to prepare for a job interview arrowright the importance of studying a foreign language arrowright reset

The teacher didn't explain this at all and i don't understand this