Question

the innocence of youth throws around it ______ charm; it demands respect and restraint. source: memoirs of casanova — volume 20: milan a diversified an ineffable a figurative a nocturnal

Explanation:

The word "ineffable" means too great or extreme to be expressed or described in words. The innocence of youth is said to have a charm that is beyond description, which makes "ineffable" the most appropriate choice. "Diversified" means varied, "figurative" relates to figures of speech, and "nocturnal" refers to things related to night. None of these fit the context as well as "ineffable".

Answer:

B. an ineffable