A new study brings new attention to the phenomenon of unidentified flying objects. The study reports that about 65% of Americans say that they believe that intelligent life exists on other planets. Are older Americans (over 50 years old) less likely to believe that intelligent life exists on other planets? Based on a random sample of 280 older Americans (over 50 years old), 60% say intelligent life exists on other planets.

Which of the following is a complete definition of the unknown parameter ?

Choice 1 of 4: The proportion of all Americans who believe intelligent life exists on other planets.Choice 2 of 4: The proportion of all Americans who are over the age of 50 years old.Choice 3 of 4: The proportion of all older Americans (over 50 years old) who believe intelligent life exists on other planets.Choice 4 of 4: The sample proportion of older Americans (over 50 years old) who believe intelligent life exists on other planets.