Discrete Math Interview Question:

The g -1({0}) for the function g(x)= ⌊x⌋ is ________.
a) {x | 0 ≤ x < 1}
b) {x | 0 < x ≤ 1}
c) {x | 0 < x < 1}
d) {x | 0 ≤ x ≤ 1}