Final answer:
Giblin likely views the Rosetta Stone as highly important, hence the words 'vital' and 'crucial' best describe his view on the artifact's significance in history.
Step-by-step explanation:
The words that best show that Giblin views the Rosetta Stone as very important are vital and crucial. The Rosetta Stone is a historical artifact that has played a significant role in deciphering Egyptian hieroglyphs, leading to a greater understanding of ancient Egyptian culture and language. Words such as negligible, insignificant, ordinary, common, overrated, and irrelevant do not accurately reflect the importance attributed to the Rosetta Stone by historians and scholars.