Use ‘an’ before words such as “hour” which sound like they start with a vowel even if the first letter is a consonant. Also use ‘an’ before letters and numbers which sound like they begin with a vowel, such as “F” or “8”.

The definite article ‘the’ is used before specific things. Here, we are referring to the specific time when both the speaker and Mary arrived.

The definite article ‘the’ is used before specific things. Here, we are referring to the specific ‘patriot’ that rose within the person.

The definite article ‘the’ is used before specific things. Here, we are referring to the specific ‘library’ whose location speaker wants to know.

‘An’ is an indefinite article which is used before a word that begins with a vowel sound and which refers to unspecific/general things. Here, ‘actor’ begins with a vowel sound and it is unspecific.

‘An’ is an indefinite article which is used before a word that begins with a vowel sound and which refers to unspecific/general things. Here, ‘electrician’ begins with a vowel sound and it is unspecific.

Here, a specific ‘office’ is being talked about where the second person goes. Hence, ‘the’ article will be used.

Here, ‘Umbrella’ is a general thing and therefore indefinite article will be used. Word after the blank starts with vowel sound. ‘An’ article will be used.

In the sentence it is not specified which hotel and therefore we will use indefinite article. ‘Hotel’ begins with a consonant sound and will be preceded by ‘a’ article.

‘Thar desert’ is a specific desert and definite article should be used. Hence, ‘the’ article is correct.