Answer:
B. External validity
Step-by-step explanation:
External validity- It refers to the extent through which a conclusion made from the research study can be generalized to the person outside the study.
Generalization is of three types: environmental, temporal, and population.
Threats to external validity:
1. History effects & maturation.
2. Selection biases.
3. Constructs, confounding, and methods.
4. The 'experimental world' versus the 'real world'.