The correct answer is option 'C', the river that borders the Meghalaya-Mikir Uplands in the east is the Dhansiri River. Let's delve into the details explaining this answer:

Introduction:
The Meghalaya-Mikir Uplands is a region located in the northeastern part of India, primarily covering parts of the states of Meghalaya and Assam. It is known for its hilly terrain, rich biodiversity, and scenic beauty. Several rivers and streams flow through this region, providing water resources and shaping the landscape.

The Dhansiri River:
One of the prominent rivers that borders the Meghalaya-Mikir Uplands in the east is the Dhansiri River. The Dhansiri River is a major tributary of the Brahmaputra River, which is one of the largest rivers in Asia. It originates from the Borail Range of the Patkai Hills in Nagaland and flows through parts of Assam and Nagaland.

Significance of the Dhansiri River:
1. Geographical Boundary: The Dhansiri River forms the eastern boundary of the Meghalaya-Mikir Uplands, separating it from the neighboring areas.
2. Water Resources: The river serves as a crucial water resource for the region, supporting agriculture, fishing, and other livelihood activities.
3. Biodiversity: The Dhansiri River and its surrounding areas are home to diverse flora and fauna. The river's ecosystem supports various aquatic species, birds, and mammals.
4. Irrigation and Hydropower: The Dhansiri River is utilized for irrigation purposes, facilitating agricultural practices in the region. It also has the potential for hydropower generation.

Conclusion:
In conclusion, the Dhansiri River is the river that borders the Meghalaya-Mikir Uplands in the east. It plays a significant role in defining the geographical boundary, providing water resources, supporting biodiversity, and facilitating agricultural and hydropower activities in the region.