The correct answer is option 'A', Bangladesh.

The Ichhamati River is a trans-boundary river that flows between India and Bangladesh. It is an important river in the South 24 Parganas district of West Bengal, India, and eventually joins the Hooghly River. Let us delve into the details of this river and its significance.

River Description:
The Ichhamati River originates from the Barasat District in West Bengal, India. It flows through the North 24 Parganas and South 24 Parganas districts of West Bengal before crossing the international border and entering Bangladesh. In Bangladesh, it is known as the Ichamati River. The river forms a natural border between India and Bangladesh for a significant stretch.

Trans-Boundary River:
The Ichhamati River is a trans-boundary river as it flows through both India and Bangladesh. Trans-boundary rivers are those that cross national boundaries, and they often require cooperation and management between the countries involved. In the case of the Ichhamati River, India and Bangladesh need to work together to ensure the sustainable use of its water resources and to address any issues related to its flow and management.

Importance:
The Ichhamati River holds great importance for both India and Bangladesh due to its role in irrigation, agriculture, and as a waterway. It is a lifeline for the people residing along its banks as it provides water for irrigation, enabling agricultural activities and supporting the livelihoods of the local communities. Additionally, the river serves as a transportation route for goods and people, facilitating trade and commerce between the two countries.

Importance for Biodiversity:
The Ichhamati River also plays a crucial role in supporting the biodiversity of the region. The river and its surrounding wetlands provide habitats for various species of flora and fauna. The riverine ecosystem supports a diverse range of aquatic plants, fish, and other aquatic organisms. It also attracts migratory birds, making it an important site for birdwatching and conservation.

Conclusion:
In conclusion, the Ichhamati River is a trans-boundary river that flows between India and Bangladesh. It is of great significance for both countries, serving as a source of water for irrigation, supporting agriculture, and facilitating trade and transportation. The river's ecosystem also contributes to the biodiversity of the region. Cooperation and management between India and Bangladesh are essential to ensure the sustainable use of the river's resources and address any challenges related to its flow and management.