identify the characteristic of a transverse wave that doubled from wave a to wave b.\na amplitude\nb…

Brief Explanations:

The amplitude of a transverse wave is the maximum displacement from the rest - position. Comparing wave A and wave B, the height from the rest - position to the crest (or trough) of wave B is twice that of wave A. Crest and trough are parts of a wave, not characteristics that can double in this context. Wavelength is the distance between two consecutive crests or troughs and it doesn't double here.

Answer:

A. amplitude