The unique living root bridges found in Meghalaya are often built across:

The correct answer is: c) Rivers.

Living root bridges are unique to the Khasi and Jaintia hills of Meghalaya, India. They are made by planting the roots of rubber fig trees (Ficus elastica) over a period of many years. The roots grow into the soil on the opposite bank of the river, and eventually form a bridge that can support the weight of people and animals.

Living root bridges are an important part of the culture of the Khasi and Jaintia people. They are used as a means of transportation, and they also play a role in religious ceremonies.

The other options are incorrect because:

• Lakes are not typically wide enough to require a bridge.
• Canals are man-made waterways, and living root bridges are not typically built across them.
• Reservoirs are artificial lakes, and living root bridges are not typically built across them.