Final answer:
The correct pronoun to complete the sentence 'He saw us' is 'us'.
Step-by-step explanation:
The correct pronoun to complete the sentence 'He saw us' is us. The pronoun 'us' is used to refer to the person(s) being seen, in this case, the speaker and others. For example, if the sentence was 'He saw me', it would mean that only the speaker was seen. Similarly, if the sentence was 'He saw them', it would mean that other people were seen but not the speaker.
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