Select the most appropriate option to substitute the underlined segment in the given sentence. If no substitution is required, select 'No replacement required'.

The supervisor recommended that he attends the safety briefing immediately.

The correct option is that he attend the safety briefing.

Explanation:
1. Understanding the Subjunctive Mood: Certain verbs that express a recommendation, suggestion, command, or requirement—such as recommend, suggest, insist, demand, and propose—require the verb in the following that-clause to be in the subjunctive mood.
2. Form of the Subjunctive: The present subjunctive always takes the base form of the verb (the bare infinitive without 'to') regardless of the subject. Even though the subject is the third-person singular pronoun he, the verb must remain in its base form attend (rather than "attends" or "attended").
3. Corrected Sentence: "The supervisor recommended that he attend the safety briefing immediately."

Reasoning for incorrect choices:
- No replacement required / that he attends the safety briefing: Incorrect because "attends" uses the simple present indicative instead of the required subjunctive base form.
- that he has attend the safety briefing: Incorrect due to ungrammatical verb structure ("has attend").
- that he attending the safety briefing: Incorrect because the participle "attending" cannot function as the finite verb of the clause.
- that he attended the safety briefing: Incorrect because past tense does not express the mandated subjunctive mood required after verbs of recommendation.