Divide the words into two groups: with a or an

• Группы
  • a
  • an
• Варианты
  • pencil sharpener
  • ruler
  • pencil case
  • notebook
  • blackboard
  • book
  • school bag
  • pen
  • timetable
  • eraser
  • atlas
  • object
  • apple
  • exam
  • exercise book