input: Write a function that takes an integer `gross_sales` and returns the corresponding commission rate based on specified conditions, but make the function more efficient by directly returning the rate when the condition is met.
  
  The function should follow these rules:
  - If `gross_sales` is greater than or equal to 10000, the function should return 0.1.
  - If `gross_sales` is between 5000 and 10000, the function should return 0.07.
  - If `gross_sales` is less than 5000, the function should return 0.05.
  
  Assert test cases to verify the functionality of the function are as follows:
  assert determine_commission_rate(15000)==0.1
  assert determine_commission_rate(7500)==0.07
  assert determine_commission_rate(4500)==0.05
  assert determine_commission_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
      else:
          return 0.05