Question

complete the sentence.
bernie knew that he had heard the word auspicious before and vaguely understood the meaning, but he could neither think of a synonym nor
__________________________.
use the word in a sentence
could he use the word in a
sentence

Explanation:

When using the structure "neither...nor", if the first part ("think of a synonym") is in the base form (no auxiliary verb), the second part should also follow the same structure. "Could he use..." is a question - like structure which is not parallel. "Use the word in a sentence" maintains parallelism with "think of a synonym".

Answer:

use the word in a sentence