Why is instrumentation a potential threat to validity in a time-series design?

A) When participants take the same measures over and over again, they tend to get "better" at them.
B) When people initiate new approaches or programs, there also may be accompanying changes in the way records are made and kept.
C) The more times something is measured, the less reliable it is.
D) When a study is carried out over a long period of time, participants tend to drop out or leave.

Answer: B