Select the most appropriate option that can substitute the highlighted segment in the given sentence. If there is no need to substitute it, select ‘No replacement required’.
She suggested that he goes to the doctor immediately.

The correct option is "that he go to the doctor".

Step-by-Step Explanation:
1. Identify the verb triggering the mood: The main verb in the sentence is "suggested". Verbs that express a suggestion, recommendation, demand, or necessity (such as suggest, recommend, insist, demand, propose, or advise) followed by a "that"-clause require the subjunctive mood in English.
2. Apply the subjunctive rule: In the subjunctive mood, the verb in the "that"-clause must always be in its base form (the bare infinitive, e.g., go, be, do, study), regardless of the subject's grammatical person or number (whether singular or plural).
3. Analyze the options:
- "that he goes to the doctor" (Original): Uses the indicative present form "goes" for the third-person singular subject "he", which is grammatically incorrect in a subjunctive clause.
- "that he go to the doctor": Uses the base form "go" of the verb, which correctly satisfies the subjunctive mood requirement.
- "that he gone to the doctor": Grammatically incorrect as "gone" is a past participle and cannot function as a finite verb on its own here.
- "that he had go to the doctor": Grammatically incorrect structure.
- "that he went to doctor": Lacks the definite article "the" before "doctor" and uses the past indicative "went" instead of the required subjunctive base form.

Therefore, the highlighted segment must be substituted with "that he go to the doctor" to make the sentence grammatically correct: "She suggested that he go to the doctor immediately."