input: Write a function to determine_commission_rate(gross_sales) that returns the commission rate based on given sales amounts. If gross_sales is 10000 or higher, the function should return 0.1. If gross_sales is between 5000 and 9999 (inclusive), the function should return 0.07. If gross_sales is less than 5000, the function should return 0.05. The function should be optimized to return the result directly within the conditional statements.
  
  assert determine_commission_rate(15000)==0.1
  assert determine_commission_rate(7500)==0.07
  assert determine_commission_rate(4000)==0.05
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