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A prerequisite knowledge graph of 1590 learning concepts across 8subjects. Track what you've mastered and see exactly what you're ready to learn next — the topics whose prerequisites you've already met. Built on the Marble Open Skill Taxonomy.

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Choosing A or An

English · Grammar & Punctuation · language

Use the correct form of the indefinite article — 'a' before words beginning with a consonant sound and 'an' before words beginning with a vowel sound (e.g., a rock, an open box, an hour, a unicorn)

What mastery looks like

  • Choose 'a' or 'an' correctly before nouns beginning with consonant or vowel sounds (e.g., 'a ball', 'an egg', 'an umbrella')
  • Apply the rule to tricky words where spelling and sound differ (e.g., 'an hour' because /h/ is silent, 'a uniform' because /juː/ starts with a consonant sound)
  • Correct errors in a/an usage in given sentences (e.g., change 'a orange' to 'an orange')

Check your understanding

When Choosing A or An writes, do they automatically choose "a" before a word that starts with a consonant sound and "an" before a vowel sound — like "a cat" but "an apple" or "an hour"?

Prerequisites

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