The correct answer is option 'D' - Army.

Explanation:
The protest movement mentioned in the question refers to a hypothetical situation where various organizations or institutions come together to protest against a particular issue. Among the given options, the organization that did not join the protest movement is the Army.

Here is a detailed explanation of each option and why the Army did not join the protest movement:

a) Labour unions and their federations:
Labour unions and their federations are organizations that represent the interests of workers and advocate for their rights. They often engage in collective bargaining, strikes, and protests to address issues related to working conditions, wages, and benefits. Given their focus on workers' rights, it is highly likely that labour unions and their federations would join a protest movement to support their members or address broader issues affecting workers.

b) Organisation of indigenous people:
The organization of indigenous people represents the rights and interests of indigenous communities. They often advocate for land rights, cultural preservation, and protection against discrimination. Indigenous communities have historically faced marginalization and injustice, making them more likely to participate in protest movements to highlight their grievances and demand change.

c) Organisation of teachers, lawyers, and human rights groups:
These organizations represent professionals in their respective fields and often work towards advocating for their members' rights or promoting social justice. Teachers' organizations may protest against education policies, lawyers may protest against the violation of legal rights, and human rights groups may protest against human rights abuses. Given their focus on social justice issues, it is highly likely that these organizations would join a protest movement.

d) Army:
The Army, as an institution, is primarily responsible for national defense and maintaining internal security. While individual members of the Army may hold personal opinions and participate in protests in their capacity as citizens, the Army as an institution typically remains politically neutral and avoids direct involvement in protest movements. This is because the Army is bound by strict hierarchical structures and is expected to follow orders from the civilian government. Engaging in protest movements could undermine the chain of command and the principle of civilian control over the military. Therefore, it is less likely that the Army as an institution would join a protest movement.

In summary, while labour unions, organizations of indigenous people, and organizations of teachers, lawyers, and human rights groups are more likely to join a protest movement, the Army, as an institution, typically remains politically neutral and avoids direct involvement in such movements.