Final answer:
Creep can indeed occur on gentle slopes; this is true. The statement about a rock thrown in the air increasing its kinetic energy with height is false, as it gains potential energy instead. The statement about wave amplitudes is also false, as they can add up regardless of propagation direction.
Step-by-step explanation:
Creep can occur on even very gentle slopes. This statement is True. Creep, also known as soil creep or solifluction, is a slow, downward progression of soil or rock in any environment. A perfect example of creep can be seen in terraces created on grassy slopes during the freeze-thaw cycles, where the soil expands due to ice formation and contracts when it thaws.
As for the statement that a rock thrown into the air will increase its kinetic energy with height and then increase its potential energy as it falls to the ground, this is False. It's actually the opposite – when a rock is thrown into the air, it loses kinetic energy as it gains height which increases its potential energy and then gains kinetic energy as it loses potential energy while falling.
Furthermore, it is False that the amplitudes of waves add up only if they are propagating in the same line. This may refer to the principle of superposition, which is valid for all waves regardless of their propagation direction.