Step 1: Understanding the Concept:
This question tests the use of indefinite articles ('a' and 'an'). The choice between 'a' and 'an' depends on the sound of the first letter of the word that follows.
Step 2: Detailed Explanation:
- We use the article 'a' before words that begin with a consonant sound (e.g., a boy, a car, a university).
- We use the article 'an' before words that begin with a vowel sound (a, e, i, o, u) (e.g., an apple, an hour, an honest man).
The word "island" starts with the letter 'i', which has a vowel sound. Therefore, the correct article to use is 'an'.
The complete sentence is: "Sri Lanka is an island."
Step 3: Final Answer:
The correct option is (B) because the word "island" begins with a vowel sound.