Fork help

Programming help..
  A
/ | \
B C D
 / \ \
 E F  G
For our assignment we are supposed to (in writing) say how we can perform the creation of said processes using 6, 5, 4, and 3 fork calls. I can understand 6 calls easy enough, but I am a little confused on how to accomplish it with less.

My basic thought is to do the initial fork, then if the pid is 0 do some condition to fork again.. but I am a little confused. Any help would be appreciated. I don't need the code, and I don't need all of the solved, just a little push in the right direction.

Here is a dot version of your directed acyclic graph
File: fork.dot
digraph Hierarchy {
  rankdir=TB;
  "A"->"B";
  "A"->"C";
  "A"->"D";
  "C"->"E";
  "C"->"F";
  "D"->"G";
}

Invoke with $ dot -Txlib fork.dot.