Answer
Peak height, largest to smallest: A, B, D, C.
Work Step by Step
When the center of the pulses coincide, the waves will add algebraically to determine the height of the peak.
In picture A, both peaks are positive,with heights of about +1 and +2 units. They add to a greater height than the two smaller positive peaks (1+1) in picture B.
In picture C, the pulses are equal and opposite (1 and -1), and will add to a peak height of zero.
In picture D, the negative pulse (-2) is larger than the positive pulse (+1), and the resulting peak will be negative, thus having a "lower height" than the zero height in C.
The question is a little ambiguous: if peak "size/magnitude" is the intention, the order should be A, B, D, C.
