In the following question, out of the four alternatives, choose the one which can be substituted as a single word for the description: "A person who opposes war or the use of military force."

Introduction / Context:
This question belongs to the important English vocabulary area of one-word substitutes. Competitive exams frequently test your ability to replace long descriptive phrases with a precise single word. Here, you are given the description "A person who opposes war or the use of military force" and asked to choose the correct one-word substitute from the options.

Given Data / Assumptions:

• We are looking for a one-word substitute.
• Description: a person who opposes war.
• The person also opposes use of military force in general.
• Four given options: Narcissist, Fatalist, Pacifist, Fascist, plus one extra plausible looking word.
• We assume standard modern English usage as in exam level vocabulary books.

Concept / Approach:
The key concept here is ideological opposition to war and violence. In political and moral vocabulary, a person who believes that disputes should be settled peacefully and who is against war and military methods is called a "pacifist". The word comes from "peace". A pacifist favours negotiation, non violence, and diplomacy rather than armed conflict. The correct option must clearly reflect this meaning, and not be confused with words about self love, fate, or dictatorship.

Step-by-Step Solution:
Step 1: Underline the key idea in the description: opposes war and military force.Step 2: Recall relevant ideological words such as pacifism, militarism, fascism, nationalism, and so on.Step 3: Remember that a follower of pacifism is called a pacifist.Step 4: Check the options: only "Pacifist" directly relates to peace and opposition to war.Step 5: Confirm that this word perfectly fits the description given in the question.

Verification / Alternative check:
Use the word in a sentence: "As a pacifist, she refused to support any war." This matches the idea of someone who opposes war and military action. Now try substituting each option into a similar sentence. "As a narcissist, she refused to support any war" focuses on self love, not opposition to war. "As a fatalist" shows belief in fate, not necessarily peace. "As a fascist" actually implies support for authoritarian rule and often aggressive nationalism, which is the opposite of pacifism. Therefore, only "pacifist" correctly reflects the described person.

Why Other Options Are Wrong:

• Narcissist: A narcissist is someone who has excessive self love and vanity. This has nothing to do with attitudes towards war.
• Fatalist: A fatalist believes that all events are predetermined and inevitable. This is a philosophical position, not specifically a stance against war.
• Fascist: A fascist supports a dictatorial, extreme right wing system. Fascist regimes are usually militaristic, not opposed to war.
• Realist: A realist focuses on practicality and actual conditions, not on ideal visions of peace. The word does not mean opposition to war.

Common Pitfalls:
Students sometimes confuse "pacifist" with "fascist", because both words sound somewhat similar. Always focus on the root: "pac" in pacifist connects with "peace", while "fasc" in fascist relates to authoritarian politics. Another mistake is to choose an option just because it looks sophisticated. The best strategy is to connect the description with known roots and meanings.

Final Answer:
The correct one-word substitute for a person who opposes war or the use of military force is Pacifist.