The correct answer is that young people are the ones who are the least likely to have an influence on public policy. Young people do not vote as often as older people do so politicians are less likely to value their opinions. In addition, young people are not generally as well-educated as older people and lack the levels of life experience that make people pay attention to what they say. Therefore, they can have less influence on the thoughts of other people.
The other options here are wrong. Opinion leaders are, by definition, influential. Other people pay attention to what those people think. The wealthy and the well-educated tend to be more highly respected in our society. People think that these people must know more because they have gone to school for a long time or because they have managed to become rich. Either way, people are more likely to respect the opinions of rich and/or educated people than they are to respect the opinions of young people. This is why “young people” is the correct answer.