| 1. I have a / an sister. |
| 2. It is a / an book. |
| 3. A / an elephant is grey. |
| 4. I have an / a green airplane. |
| 5. She has a / an desk in her room. |
| 6. We've got an / a airplane. |
Explanation:
We use 'a' before words that start with a consonant sound and 'an' before words that start with a vowel sound. In the sentences above, the correct articles have been underlined based on this rule.