<p>Attending conferences relating to their fields can help <strong>widen</strong> people's professional networks.</p>
<p>The correct answer is <strong>(B) widen</strong>.</p>
<p>In this sentence, we need to use the verb form that matches the subject "Attending conferences." The subject is in the present tense and is referring to a general action that can be done by people in general. Therefore, we need to use the base form of the verb, which is "widen."</p>
<p>Option (A) "wide" is an adjective, not a verb, so it is incorrect.</p>
<p>Option (C) "wider" is the comparative form of the adjective "wide," and it does not fit grammatically in this sentence.</p>
<p>Option (D) "widely" is an adverb, which modifies verbs, adjectives, or other adverbs. In this sentence, we need a verb form, not an adverb.</p>