Network printer VS Ordinary

Suppose John plans to buy a new printer and wants to share it with Sally. He considers two different types of printer: a network printer (N-printer) and an ordinary printer without any network connection capability (O-printer). Consider the following printer connection layouts A, B, C, and D.

The layout is shown in
http://i.cs.hku.hk/~whcheng/temp/q.jpg

Question 1: Why is only layout A, C, D can support the sharing of the printer between John and Sally?

Question 2: Suppose Susan wants to prints things in layout D, the job first pass through hub and then broadcast to Jack's computer. Why does Jack's computer knows that it should be passed to O-printer? (based on MAC address of O-printer??)

Question 3: Which one is the best layout for printer sharing? Why?