Final answer:
The sentence 'The books (lose) in the port. (Past)' is correctly completed in the passive voice with the option 'were lost'. Passive voice construction includes the subject being acted upon, the use of a form of 'to be', and the past participle of the main verb, with the 'by' preposition indicating the doer.
Step-by-step explanation:
The correct completion for the sentence 'The books (lose) in the port. (Past)' in the passive voice is 'were lost'. We can determine the passive voice in a sentence by identifying whether the subject is being acted upon, the use of a form of the verb 'to be' with a past participle, and the possible presence of the preposition 'by' followed by a noun phrase. For instance, 'That his house was no place for a dance party was argued by Jose' shows the subject (the house) is being acted upon by something else (Jose), uses the past tense of 'to be' (was), and includes the preposition 'by' indicating who performed the action. Therefore, the complete sentence in passive voice and in past tense is 'The books were lost in the port'.