Passive voices can be present, past, with modals and stative passive. The correct blank is <u>could be seen</u>.
<h3>What are modals?</h3>
Modals are the verb form that represents the ability, necessity, and intent in the sentence of another verb form. Some examples of models are could, can, might, would, must, etc.
Modals are used with passive voice in sentences as object + modal + be + past participle form of the verb. hence the sentence will include could (modal) + be and seen (past participle).
Therefore, the correct blank is <u>could be seen.</u>
Learn more about modals here:
brainly.com/question/6250914
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