Fill in the blank with the suitable article: I met ___ old man in the train.

Answer: an

Rule: Use 'an' before words that begin with a vowel sound.

Why this fits: The word 'old' begins with a vowel sound, so the correct phrase is 'an old man.'

• Why 'a' is incorrect: 'a' goes before consonant sounds (e.g., 'a young man').

• Why 'the' is incorrect: 'the' is definite and refers to a specific known person (e.g., 'the old man we saw earlier'), but the sentence introduces an unspecified person.

• Why 'some' is incorrect: 'Some' is used with plural or uncountable nouns, not with a singular countable noun like 'man'.

Tip: Decide by sound, not spelling. If the next word starts with a vowel sound, use 'an'; otherwise use 'a'.