$10 - 1 = 9$ 
There are $10$ trees on one side of a road. Workers plan to set one rubbish bin bwtween every two adjacent trees. How many rubbish bins do they need to prepare? 

  * $$8$$ 
  * $$9$$ 
  * $$10$$ 
  * $$11$$ 
  * $$12$$ 