The correct answer is $\boxed{\text{C) 90°}}$.
Two waves are said to be in phase if they reach their maximum and minimum values at the same time. They are said to be out of phase if they reach their maximum and minimum values at different times. The phase angle is the difference between the phases of two waves.
In this case, one wave attains its maximum value while the other is at zero value. This means that the first wave is 90 degrees ahead of the second wave. Therefore, the phase angle between the two waves is 90 degrees.
Option A is incorrect because 0 degrees is the phase angle between two waves that are in phase. Option B is incorrect because 45 degrees is the phase angle between two waves that are in quadrature. Option D is incorrect because 180 degrees is the phase angle between two waves that are opposite in phase.