Although 'useful' begins with 'u', it has a 'yoo' consonant sound. This requires 'a'. 'An useful example' would be wrong. Since it is introduced for the first time, the indefinite article is suitable. Thus, 'a useful example' is correct.

A specific playground is being referred to, so 'the' is required. The definite article makes the meaning precise. 'A playground' would mean any playground. 'An playground' would be wrong grammatically. Hence, 'the playground' is correct.

The noun 'eagle' begins with a vowel sound, so 'an' is correct. Since this is the first mention, the indefinite article fits. 'A eagle' would be grammatically incorrect. 'The eagle' would imply one already specified. Therefore, 'an eagle' is correct.

The compound begins with 'one', which has a consonant 'w' sound. This makes 'a' the correct article. 'An one-liter bottle' would be incorrect. 'The bottle' would suggest one already specified. Thus, 'a one-liter bottle' is correct.

The stars in the sky are a universal reference, so the definite article 'the' is needed. This narrows the meaning to the stars visible in the night sky. 'A stars' would be grammatically wrong. 'No article' would leave the sentence incomplete. Therefore, 'the stars' is correct.

Although 'university' begins with the letter 'u', it has a consonant 'yoo' sound. Therefore, 'a' is correct. 'An university' would be grammatically wrong. Since this is the first mention, the indefinite article is appropriate. Hence, 'a university hostel' is correct.

The word 'inspiring' begins with a vowel sound, so 'an' is correct. Indefinite articles are used for first-time mentions. 'A inspiring lecture' would be grammatically incorrect. 'The lecture' would only work if it were already known. Therefore, 'an inspiring lecture' is correct.

Sacred texts like the Quran always take the definite article 'the'. This emphasizes their uniqueness and reverence. 'A Quran' or 'an Quran' would be grammatically wrong and contextually inappropriate. 'No article' would also leave the sentence incomplete. Thus, 'the Holy Quran' is correct.

The noun 'owl' begins with a vowel sound, so 'an' is required. Indefinite articles are correct when introducing something for the first time. 'A owl' would be grammatically wrong. 'The owl' would imply one already known in the context. Thus, 'an owl' is correct.

Names of seas and oceans always take the definite article 'the'. The Red Sea is a unique geographical feature. 'A Red Sea' or 'an Red Sea' would be ungrammatical. 'No article' would leave the sentence incomplete. Hence, 'the Red Sea' is correct.