Waves begin to "feel bottom" when the depth of water is equal to the wavelength equal to its wave base twice as great as the wavelength three times as great as the wavelength

None of the listed options

Explanation:

None of the listed options is right.

The right answer is

Waves began to feel bottom when the depth of the water is "equal to one half of the wavelength"

This is so because;

The speed of a wave and its variation is dependent on the wavelength.

Wave sails at a faster rate, if the wave sails in deeper water.

At this point, the height it reaches will be lower than if it travels at a reduced speed.

In other words, the more the waves move closer in proximity to shallow water, it gradually changes to breaking waves.

As deep-water wave reaches shore, at the point where the depth of the water is one-half of the wave's length, it begins to "feel" the bottom.

Conclusively, whe water is one half of the wavelength of the wave when it approaches the ocean floor. These waves are referred to as shallow-water waves.

So, none of the options above is correct.