What is the shortest path that will visit point A, B, C, and D?

https://dw6y82u65ww8h.cloudfront.net/organisations/328/94ce962c-bb45-4cbb-8c4a-2b1e1ed75681/img_quad_vertexedge_d.gif

link to graph

A to D to C to B
C to B to D to A
B to A to D to C
A to B to C to D