Choose the one word that best replaces the given description: Bitter quarrel between two families existing for a long period.

Introduction / Context:
This question tests knowledge of one word substitutions related to conflict and relationships. The description mentions a bitter quarrel between two families that lasts for a long period. Such conflicts may span generations and involve deep resentment. English has a specific word for this type of prolonged hostility between families or groups, and recognising it is important for precise vocabulary use.

Given Data / Assumptions:

• The quarrel is described as bitter, indicating strong hostility.
• It involves two families, suggesting a social or personal conflict, not entire nations.
• The quarrel continues for a long period, which implies long term hostility, sometimes across generations.
• Options given are siege, feud, battle, and war.

Concept / Approach:
The word feud refers to a long lasting and bitter quarrel or hostility between families, clans, or groups. Famous examples include historical family feuds. Siege, battle, and war are terms from military language. A siege is a military operation surrounding a place. A battle is a single fight between armed forces. War is prolonged armed conflict between countries or large groups, but not limited to two families. Therefore, feud is the only word that matches the personal, long term, family based conflict described in the question.

Step-by-Step Solution:
Step 1: Note that the conflict involves families, not countries or armies. Step 2: Note that it is bitter and long lasting, which suggests deep, personal resentment. Step 3: Recall that feud is defined as a prolonged and bitter quarrel or conflict between families or clans. Step 4: Examine siege and observe that it is a military term for surrounding a place to force surrender. Step 5: Examine battle, which means a single armed conflict or fight between forces, usually brief compared with a long family quarrel. Step 6: Examine war, which refers to overall armed conflict between nations or large groups, not typically used for personal family disputes. Step 7: Conclude that only feud fits all aspects of the description given in the question.

Verification / Alternative check:
Think of example sentences: The two families have been locked in a feud for decades describes exactly the situation in the question. In contrast, it would be unusual to say The two families are in a war or a battle in normal social contexts. Dictionaries also emphasise that feud often refers to long standing hostility between families or clans, which matches perfectly.

Why Other Options Are Wrong:
Siege is wrong because it is a specific military tactic and requires forces surrounding a fortified place. Battle is wrong because it generally refers to a single engagement in war, which is short in duration. War is wrong because it denotes large scale armed conflict between nations or large groups, not personal family quarrels. None of these express long term, family based hostility as accurately as feud.

Common Pitfalls:
Some students pick war or battle because they associate bitterness with violent conflict and ignore the family context. Others may not notice the long period aspect, which is crucial for the word feud. To avoid mistakes, read all parts of the description carefully, especially clues about who is involved and how long the conflict lasts.

Final Answer:
The correct one word substitution for a bitter, long lasting quarrel between two families is feud.