Final answer:
The missing word in the sentence of the passage is 'to'. This forms the sentence 'The day of the dance, I was horrified to find a big red splotch on my face'. The word 'to' introduces the infinitive 'to find', indicating the reason for the speaker's horror.
Step-by-step explanation:
In the provided passage, the missing word should be 'to'. So, the complete sentence reads: 'The day of the dance, I was horrified to find a big red splotch on my face'. The word 'to' is needed after the word 'horrified' because it introduces the infinitive verb form 'to find'. This sentence structure is commonly used to express reactions to situations.
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