The horizontal distance between the a crest and an adjacent trough of either waveform is approximately $3 \mbox{ cm}$ . If the waveform in channel 1 is shifter approximately $2 \mbox{ cm}$ , then it will align with the waveform in channel 2. So, the phase difference between the two waveforms is approximately
$\begin{align*}2 \mbox{ cm} \cdot \frac{180^{\circ}}{3 \mbox{ cm}} = \boxed{120^{\circ}}\end{align*}$
Therefore, answer (E) is correct.

Solution to 2008 Problem 42