Final answer:
To complete the sentence with an intensive pronoun, you should say 'You can only be a witness if you yourself have seen the crime.' The word 'yourself' serves to emphasize that the speaker is the one who must have seen the crime in order to be a witness.
Step-by-step explanation:
To complete the sentence with an intensive pronoun, you should use a pronoun that emphasizes the subject, which in this case is 'you'. An intensive pronoun is used for emphasis on the subject that has already been named. It is not essential to the meaning of the sentence, but it provides additional emphasis that the subject themselves is directly involved in the action.
The sentence completed with an intensive pronoun would be: You can only be a witness if you yourself have seen the crime.
Intensive pronouns often reflect back on the subject of the sentence, which in this case is 'you'. Therefore, 'yourself' is correct because it is reflective of 'you' and provides the necessary emphasis on the subject who must have seen the crime to be a witness.
The correct intensive pronoun to complete the sentence would be yourself. The sentence would then read: "You can only be a witness if you yourself has seen the crime." Intensive pronouns are used to emphasize the noun or pronoun they refer to. In this case, "yourself" emphasizes the pronoun "you."