Which of the Following Is the Best Example of the Observational

Which of the following is the best example of the observational method?

A) Chris puts a glass to the wall so that he can hear his parents argue.
B) Xena sends out a questionnaire to gain information on people's eating habits.
C) Gary stops people on the street to ask them how they voted in the last elections.
D) Twyla secretly videotapes guests at her sister's wedding.
E) Elaine parks her car near a traffic light and records how many drivers run red lights.