Using variables

Which of the following statements is true?
  1. variables have names
  2. variables have data types
  3. variables have values
  4. variables use memory
  5. variables use storage
  6. all variables use the same amount of memory
  7. all variables use the same amount of storage
  8. once set, variable values never change
  9. once set, variable values cannot change until a new event occurs
  10. variable values can change as often as the programmer wishes
What is the key difference between variables and constants?

What do variables and constants have in common?