code: def simple_flow_graph():
      G = nx.DiGraph()
      G.add_node("a", demand=0)
      G.add_node("b", demand=-5)
      G.add_node("c", demand=50000000)
      G.add_node("d", demand=-49999995)
      G.add_edge("a", "b", weight=3, capacity=4)
      G.add_edge("a", "c", weight=6, capacity=10)
      G.add_edge("b", "d", weight=1, capacity=9)
      G.add_edge("c", "d", weight=2, capacity=5)
      return G
  
imports: import bz2
  import importlib.resources
  import os
  import pickle
  import pytest
  import networkx
label_desc: Use image node_id 1 for calling a global function with example usage: simple_flow_graph() and returns: G