For a two-body system, the input of the wave function is the positions of these two particles in real space. r1 = (x1, y1, z1), r2 = (x2, y2, z2); the output is a complex number, whose amplitude indicates the probability of the configuration (r1, r2) for this system. Therefore the wave function for a two-body system is a map from R^6 to C^1. The answer should be C.