The correct answer is: a) Tea plantations.
Tea plantations were the first major industry in Assam, and they gave rise to major workers’ movements in the late 19th and early 20th centuries. The workers on these plantations were often exploited and underpaid, and they began to organize themselves to demand better working conditions. These movements were successful in achieving some reforms, but they also led to violence and repression.
The oil industry is another major industry in Assam, but it did not give rise to major workers’ movements in the same way as tea plantations. This is likely because the oil industry was not as labor-intensive as tea plantations, and the workers were not as easily exploited.
The timber trade and jute cultivation are also important industries in Assam, but they have not given rise to major workers’ movements. This is likely because these industries are not as well-organized as the tea industry, and the workers are not as easily mobilized.
In conclusion, the development of tea plantations gave rise to major workers’ movements in Assam. These movements were successful in achieving some reforms, but they also led to violence and repression.