Final answer:
The correct article to complete the sentence 'Necesito lápiz para escribir' is 'un'.
Step-by-step explanation:
The correct article to complete the sentence 'Necesito lápiz para escribir' is 'un'. In Spanish, the article 'un' is used with singular masculine nouns. Since 'lápiz' is a singular masculine noun, the correct article is 'un'. The sentence would then be 'Necesito un lápiz para escribir,' which translates to 'I need a pencil to write.'
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