Two waves that have exactly the same wavelength, frequency, and amplitude are occupying the same space. If the second wave follows exactly half a wavelength behind the first, what is true of the resulting wave? The resulting wave has zero amplitude.
The resulting wave has zero amplitude.

The resulting wave has twice the amplitude of the original waves.
The resulting wave has twice the amplitude of the original waves.

The resulting wave has zero wavelength.
The resulting wave has zero wavelength.

The resulting wave has a wavelength twice as long as the original waves.