When research results are externally valid, it means they "can be generalized to a larger population." The correct option is a.
External validity refers to the extent to which the findings of a study can be generalized or applied beyond the specific conditions or participants involved in the research.
If research results are externally valid, it indicates that the findings are likely to be relevant and applicable to a broader population or real-world situations, enhancing the generalizability of the study.
This is crucial for the practical utility and impact of research findings, as it allows for the meaningful application of results to a wider context or population beyond the study sample.