Fill in the blank with the correct option:-

The two friends appear to have fallen ______________ over a minor issue.

The correct option is out.

Step-by-step Explanation:

1. Analyze the Context: The sentence refers to "two friends" and "a minor issue." The blank requires a word that combines with the verb "fall" (here in its past participle form "fallen") to create a phrasal verb that describes a relationship dynamic affected by a disagreement.
2. Examine the Phrasal Verb Meanings: We can determine the correct word by looking at how each option changes the meaning of "fall":
• Fall out (with someone): This is an idiomatic phrasal verb that means to have an argument, quarrel, or disagreement, resulting in a damaged relationship or friendship. This perfectly matches the context of friends arguing over a minor issue.
• Fall down: This means to drop to the ground or collapse physically (e.g., "The old building fell down"). It does not apply to a conflict between friends.
• Fall into: This means to drop inside something, or to begin doing something by chance (e.g., "to fall into a bad habit").
• Fall by: This is generally used in the phrase "fall by the wayside" (meaning to fail to continue or be neglected) and does not fit here on its own.
3. Conclusion: Since the friends had a disagreement over a minor issue, the phrasal verb "fallen out" is the only correct fit. The complete sentence is: "The two friends appear to have fallen out over a minor issue."