Two Harmonic Waves Travelling in Opposite Directions Interfere to Produce $\pi$

Multiple Choice

Two harmonic waves travelling in opposite directions interfere to produce a standing wave described by y = 2 sin ( $\pi$ x) cos (3 $\pi$ t) where x is in m and t is in s. What is the distance (in m) between the first two antinodes?

A) 8
B) 2
C) 4
D) 1
E) 0.5