Sectional interest groups are organizations that represent the specific interests of a particular section of society. They advocate for the interests and demands of their members, which can include specific industries, professions, or occupational groups. Among the options given, all three examples - trade unions, business associations, and teachers associations - can be considered as sectional interest groups.

1. Trade unions:
Trade unions are organizations formed by workers or employees in a particular industry or occupation to protect and promote their rights, interests, and welfare. They negotiate with employers on issues such as wages, working conditions, benefits, and job security. Trade unions primarily represent the interests of workers and act as a collective voice for their demands and concerns. They aim to improve the working conditions and well-being of their members.

2. Business associations:
Business associations are organizations that represent the interests of specific industries or sectors. They bring together businesses operating in the same field to collaborate, share information, and advocate for their common interests. These associations may focus on issues such as policy advocacy, regulatory reforms, market access, and industry-specific challenges. They aim to promote the growth and development of their respective industries and protect the interests of their members.

3. Teachers association:
Teachers associations are organizations formed by teachers to represent their professional interests and advocate for their rights and welfare. These associations work towards improving the working conditions, salaries, benefits, and professional development opportunities for teachers. They also engage in policy discussions and advocate for reforms in the education sector. Teachers associations play a crucial role in addressing the concerns and challenges faced by educators and promoting the overall quality of education.

In conclusion, all three options - trade unions, business associations, and teachers associations - are examples of sectional interest groups. They represent the specific interests and concerns of their members belonging to different sectors or professions. These groups play a significant role in advocating for the rights, demands, and welfare of their respective sections of society.