Which of the Following Would Most Likely Create a History

Which of the following would most likely create a history threat?

A) The weather changes between the time of the pretest date and the posttest date.
B) A person grows older between the time of the pretest date and the posttest date.
C) One of the test administrators dies between the time of the pretest date and the posttest date so the posttest is given by someone different than the pretest.
D) Research subjects learn that they are all being evicted from their homes between the time of the pretest date and the posttest date.