Step-by-step explanation:
The correct options that use past participial adjectives and passive voice are:
a) The cake is eaten.
c) The cake was eaten.
In option a), "eaten" is a past participle that functions as a past participial adjective. It describes the state or condition of the cake.
In option c), "was eaten" is in the passive voice. It indicates that the cake received the action of being eaten by someone or something.
On the other hand, options b) and d) are not grammatically correct. "Eating" in option b) is a present participle, not a past participle, and does not fit with the past tense. In option d), "was eating" is a verb form in the progressive tense, but it does not fit the context of the cake being the subject of the action.