Final answer:
The sentence contains two nouns: 'toothbrush' and 'I'
Step-by-step explanation:
In the sentence, "I forgot to pack a toothbrush on the vacation", the noun is 'toothbrush'. This is a common noun as it does not refer to any specific toothbrush. The pronoun 'I' is also a noun, specifically a personal pronoun. Both 'toothbrush' and 'I' are examples of nouns in the sentence.
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