AMC 12B 2016 Problem 23

What is the volume of the region in three-dimensional space defined by the inequalities |x|+|y|+|z| \leq 1 and |x|+|y|+|z-1| \leq 1 ?

Answer Choices
A. \dfrac{1}{6}
B. \dfrac{1}{3}
C. \dfrac{1}{2}
D. \dfrac{2}{3}
E. 1