Topic: Pair of Word,

Best Answer Explained in Below-:

The question "___ research is needed to prove this to be true." calls for an adjective that conveys the depth and breadth of research required to substantiate a claim. The correct answer, "Extensive," is appropriate because it signifies that a significant amount of research, covering a wide scope of information and data, is necessary.

In scholarly contexts, "extensive" typically refers to thorough investigations that delve deeply into existing literature, consider multiple aspects of a subject, and may involve various methodologies to arrive at robust conclusions. This level of research is often essential to ensure reliability and validity in findings, particularly when seeking to establish truth or evidence for a claim.

In contrast, the other options lack this nuanced meaning. "Extreme" may suggest a high intensity but does not necessarily imply thoroughness. "Huge" focuses on size rather than comprehensiveness, and "terrific" carries a positive connotation without addressing the amount or rigor of research required. Therefore, "extensive" is the most fitting choice to convey the idea of comprehensive and diligent investigation needed for proving a claim true.