Step 1: Understanding the Question:
This is a grammar question on identifying parts of speech.
We are given a complete sentence and must identify which of the words in the options functions as an adverb.
Step 2: Key Formulas and approach:
An adverb is a part of speech that modifies a verb, an adjective, or another adverb.
It often describes how, when, where, or to what degree an action occurs.
Adverbs of manner commonly end in the suffix "-ly".
Step 3: Detailed Explanation:
$\bullet$ Let us analyze each option's grammatical function in the sentence:
$\bullet$ "committee" is part of the compound subject "Executive Committee" and functions as a noun.
$\bullet$ "approved" is the main action of the sentence and functions as a verb.
$\bullet$ "strong" modifies the noun "objections", describing its intensity, and functions as an adjective.
$\bullet$ "reluctantly" describes the manner in which the action of "approving" was carried out by the committee. It modifies the verb "approved" and ends in "-ly", making it a classic adverb of manner.
Step 4: Final Answer:
Thus, "reluctantly" is the adverb in the sentence, which is Option (D).