The correct answer is **the** (Option 4). **Comprehensive Derivation:** The correct answer is 'the'. Explanation & Key Takeaways: • 'The' is the most appropriate choice to fill the blank. • The definite article 'the' is used before a noun when it refers to something specific. • In this sentence, there is a specific house being referred to, that is, the house of the mahout. • Hence, the completed sentence would be: "The elephant moved its trunk as it spotted its mahout approaching the house." Therefore, the correct answer is 'Option 3'. Related Concepts: • 'An' is the indefinite article and is used before words that begin with a vowel sound. It doesn't fit in this sentence context properly because we are referring to a specific house. • 'Either' is used to mean one or the other of two people or things. In this sentence, there are not two houses to choose from, so 'either' would not be appropriate. • 'Both' is used to refer to two people or things, considered and identified together. In this context, we are not referring to two houses, so 'both' will not be a correct choice. **Option Elimination:** • **Option 1 (an)**: Incorrect distractor. • **Option 2 (either)**: Incorrect distractor. • **Option 3 (both)**: Incorrect distractor. • **Option 4 (the)**: Correct Answer; accurate according to canonical reference. **Exam Trap:** Be careful of misleading distractors and subtle terminology differences. Verify core properties before selecting your answer. **Memory Booster:** Core mnemonic rule: the corresponds to Option (4).