In studies involving human subjects, there could be short-term or long-term changes in participants because of psychological changes like boredom and fatigue. This would constitute which of the following threats to internal validity?

Internal changes like boredom and fatigue over time form a maturation threat.

Maturation covers natural psychological and physical changes within participants.

History threat involves external events happening during the study period.

Selection threat arises from pre-existing differences between groups.

Instrumentation threat comes from changes in the measuring tool or observers.

Maturation effects grow stronger the longer a study continues.