It is D, wavelength is from trough to trough or peak to peak, since D means identical points of a wave, this means it will definitely match the points on the peak of the first wave and the second wave, which is defined as wavelength
I think it’s latitude because latitude is the measurement of distance north or south of the Equator. And that’s exactly what the first sentence was discussing
True. This is why cliffs change or older buildings are scuffed up. Not because of vandalism or animals it’s because small particles slowly erode away the surface.