Explanation:

- Option 1: Ghadar Party

- Established in the early 20th century, the Ghadar Party was a revolutionary group formed by expatriate Indians primarily based in North America.

- Sohan Singh Bhakna and Har Dayal were prominent members and played key roles in its activities against British colonial rule in India.

- ?? Correct Answer: Ghadar Party

- Option 2: Kisan Sabha

- Focused on peasants' rights, this was a movement mainly involving farmers in India during the British Raj.

- It was not associated with Sohan Singh Bhakna or Har Dayal.

- Option 3: Anushilan Samiti

- A revolutionary group based in Bengal during the early 20th century.

- While significant, it does not relate to the primary activities of Bhakna and Dayal.

- Option 4: Yugantar

- Another revolutionary organization in Bengal alongside Anushilan Samiti.

- Not related to Bhakna and Dayal's main activities.