The Threat to Internal Validity Called "History" Refers to

The threat to internal validity called "history" refers to

A) predictable changes in people that can be expected solely due to the passage of time.
B) events happening in the community that will change the behavior of the program participants.
C) the improved skill of the staff as they come to understand the history of the program.
D) improvement in the skills of the evaluator in measuring outcome variables.