The call to prayer (Adhan) is a specific and unique religious act, so 'the' is required. The definite article emphasizes that it is not just any sound, but a particular one. Using 'a' or 'an' would suggest one among many random calls, which is not intended. Therefore, 'the call to prayer' is correct. It specifies the known act in the context.

Superlatives like 'best' always require the definite article 'the'. This is because they refer to one unique person or thing among many. 'A best student' would be ungrammatical. 'No article' would make the sentence incorrect. Therefore, 'the best student' is the right phrase.

The word 'orange' begins with a vowel sound, which requires 'an'. This is the first mention of the orange, so an indefinite article is correct. 'A orange' would be grammatically incorrect because it does not match the sound. 'The orange' would mean a specific one known already. Hence, 'an orange' fits best here.

Natural objects like the sun, moon, and sky are unique and always take the definite article 'the'. This emphasizes that we are speaking of the only existing sky in context. 'A sky' or 'an sky' would be incorrect because there is only one. 'No article' would also make the sentence sound incomplete. Thus, 'the sky' is correct.

The word 'horse' begins with a consonant sound, which requires the article 'a'. Since the horse is being mentioned for the first time, the indefinite article is correct. 'An' would not work because of the consonant sound. If it were a horse already mentioned earlier, 'the' would be used. Hence, 'a horse' is the right option.

When we talk about reading the daily newspaper, we use the definite article 'the'. It refers to the specific newspaper that is available that day. Using 'a' would imply any newspaper in general, but the sentence context suggests a particular one. 'No article' would make the sentence incomplete. Thus, 'the newspaper' is correct.

The noun 'eagle' starts with a vowel sound, so the correct article is 'an'. Indefinite articles are used when mentioning something for the first time. 'A eagle' would be incorrect due to pronunciation rules. 'The eagle' would suggest a specific bird already known to the listener. Therefore, 'an eagle' is the proper choice.

The definite article 'the' is used because the lights in question are known to both speaker and listener — likely those in the room. Using 'a' or 'an' would indicate an unknown or unspecified set of lights. Therefore, 'the lights' is the proper usage.

'Shower' is a countable noun introduced for the first time, and it begins with a consonant sound. Therefore, the indefinite article 'a' is correct. 'An' would not suit the consonant sound, and 'the' would imply a specific shower. Thus, 'a shower' is the right choice.

Proper names of rivers always take the definite article 'the'. Since 'Nile' refers to a unique river, 'the' is necessary. Omitting the article or using an indefinite one would be incorrect. Therefore, 'the Nile' is the appropriate usage.