Stones used for the construction of retaining walls must be A. Soft B. Hard C. Light D. Heavy

The correct answer is B. Hard.

Stones used for the construction of retaining walls must be hard because they need to be able to withstand the weight of the soil and water that they will be holding back. Soft stones would not be able to withstand this weight and would eventually crumble or collapse.

Option A is incorrect because soft stones would not be

able to withstand the weight of the soil and water that they would be holding back.

Option C is incorrect because light stones would not be able to provide the necessary support for the retaining wall.

Option D is incorrect because heavy stones would be more difficult to move and would also be more likely to damage the retaining wall if they were not placed correctly.