Final answer:
The sentence 'A suspicious box was found by Miss Mendez' is written in passive voice because the subject of the sentence (the box) is receiving the action, which is indicated by the verb 'was' followed by the past participle 'found'.
Step-by-step explanation:
The sentence "A suspicious box was found by Miss Mendez" is an example of passive voice. In this construction, the subject of the sentence (the box) is not performing the action (being found), but is receiving the action. The actual doer of the action (Miss Mendez) comes after the verb, and the sentence could include the preposition 'by' to indicate that. To determine if a sentence is in passive voice, locate the form of the verb to be (am, is, are, was, were) followed by a past participle (in this case, 'found'). Additionally, if you can add 'by [noun phrase]' after the verb and it makes sense, it's likely passive voice. An active voice version of this sentence could be 'Miss Mendez found a suspicious box,' placing the doer of the action before the verb.