Answer:
1. The presence of the atmosphere makes the earth <em><u>a</u></em> unique planet.
2. Nazia will meet me in <em><u>an</u></em> hour.
3. Joseph wants to learn to play <u><em>a</em></u> musical instrument.
4. Do you know of <u><em>a</em></u> good music school?
5. Would you like <u><em>a</em></u> glass of milk or <u><em>a </em></u>cup of tea?
6. Sujatha is <em><u>an</u></em> expert at mathematics.
7. Mamata Dalai, <u><em>a </em></u>six year-old girl, has got the National Bravery Award.
8. The Gram Sabha is <u><em>an</em></u> example of direct democracy at the village level.
9. The physician taught me <u><em>an</em></u> exercise to keep my eyes healthy.
10. Ladakh is <u><em>a </em></u>cold desert.