Question

What is the subject in this sentence? Could all the chocolate ice cream have been eaten?

Answer 1

Could all the chocolate ice cream have been eaten?

- Could = modal verb.

- Have been eaten --> passive.

You could say Could all the chocolate ice cream have been eaten by someone?

In which case, the patient is acted upon [by the agent] → patient = subject.

So, the subject is all the chocolate ice cream.

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Answer 2

The ‘chocolate ice-cream’ would be the subject in this sentence.