The correct answer is d) Mustard.
Mustard is a common crop that is rotated with rice in Assam. It is a short-duration crop that can be grown in the winter season. It helps to improve the soil fertility and also helps to control weeds.
Potato is a long-duration crop that requires a lot of water. It is not a good choice for rotation with rice in Assam, as it would compete with rice for water and nutrients.
Sugarcane is a perennial crop that can be grown for many years. It is not a good choice for rotation with rice in Assam, as it would require a lot of land and would not allow for the cultivation of other crops.
Tea is a perennial crop that is grown in the hilly areas of Assam. It is not a good choice for rotation with rice in the plains of Assam, as it would require a different type of soil and climate.