I believe the answer is B.
Let's look at it with punctuation: My father, an expert in the field of astronomy, recently discovered a comet.
After reading it makes more sense to have the pauses. Hopefully that helps.
Were your question is not clear
To pick out an adverb in a sentence, you should look for words that modify a verb, Some adverbs ends with -ly.
Example 1: She sings well. (well is the adverb)
Example 2: <span> Vanessa is an extremely good dancer. (extremely is the adverb)</span>
