input: Write a function to optimize the given Python code snippet for determining commission rates based on gross sales. The function should directly return the commission rate instead of assigning it to a variable. Provide test cases with expected outputs to verify the correctness and efficiency of the modified function.
  assert determine_commission_rate(12000)==0.1
  assert determine_command_rate(7500)==0.07
  assert determine_command_rate(4000)==0.05
  assert determine_command_rate(10000)==0.1
  assert determine_command_rate(5000)==0.07
output: def determine_commission_rate(gross_sales):
      if gross_sales >= 10000:
          return 0.1
      elif gross_sales >= 5000:
          return 0.07
      elif gross_sales >= 3000:
          return 0.05
      else:
          return 0.0