key word is in the end about the red diamonds

Exceedingly___________and only reliably produced by one mine in Australia, red diamonds are second only to jadeite in terms of their rarity.


As such, they are rare. So we do need two words that show the concept or rarity

The only words among the answer choices are C and F. They are synonyms

Please ask if still, something is unclear in the question

Regards

Can this be additional clue for the answer?
only reliably produced by one mine in Australia

Since only one mine produce it, it is rare?

Exceedingly___________and only reliably produced by one mine in Australia, red diamonds are second only to jadeite in terms of their rarity.

very rare, red diamonds are second only to jadeite

if you rearrange the question this way, it makes sense

Regards

Something which is rare is also Valuable , right ? So why not "RARE" as the answer as well ?

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