ANS:D - all the above.

1. There is a balance between the frictional loss and drop in elevation of the channel: In uniform flow conditions, the energy expended due to friction between the flowing water and the channel walls is balanced by the energy lost as the water flows downstream and experiences a drop in elevation. This balance ensures that the flow remains steady and uniform along the channel. It's a fundamental principle in fluid mechanics and is crucial for understanding the behavior of flowing water in canals and channels.
2. Bed and free water surfaces of a channel are parallel to each other: In uniform flow, the water surface in an open channel aligns itself parallel to the channel bed due to the balance between gravity and the frictional resistance to flow. This phenomenon is a consequence of the equilibrium reached between gravitational force pulling water downstream and the resistance offered by the channel bed and sides. The water surface adjusts its shape until the gravitational force and resistance are balanced, resulting in parallelism between the water surface and the channel bed.
3. Bed of the channel represents the hydraulic gradient: This statement is not entirely accurate. The hydraulic gradient refers to the slope of the water surface, not the channel bed. The hydraulic gradient represents the slope of the energy grade line, which is a line representing the total head available to the fluid in a conduit, pipe, or open channel. It includes both the pressure head and the elevation head of the fluid. While the channel bed may have its own slope, it's the slope of the water surface that determines the hydraulic gradient and consequently affects the flow characteristics in the channel.