Answer:
A. It extends farthest from the horizontal axis
Explanation:
The amplitude of a wave is the measure of its peak excursion from the reference value. Here, the reference value is the horizontal axis of the graph. The wave that extends the farthest in the positive and/or negative directions is wave A. Wave A has the greatest amplitude.
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Additional comment
There are various ways to define the amplitude of the wave if it is not symmetrical about the reference line. In this case, we don't need to concern ourselves with that. The value of the amplitude here is the maximum distance from the reference line, expressed as a positive number. Wave A has an amplitude of about 2.
