The correct answer is A. Some of them imagined that they would inevitably run out of cash.
The sentence “It was imagined by some of them that they would inevitably run out of cash” is in the passive voice. This means that the subject of the sentence is not performing the action, but is instead having the action performed on it. In this case, the subject is “some of them” and the action is “imagining”. The sentence can be rewritten in the active voice as “Some of them imagined that they would inevitably run out of cash.”
The other options are incorrect because they do not accurately reflect the meaning of the sentence. Option B, “They imagined that they would inevitably run out of cash,” is the closest to the correct answer, but it is not grammatically correct. Option C, “They imagined that they would not have an immense supply of cash with them,” is incorrect because it does not mention that the people imagined that they would run out of cash. Option D, “They imagined that they would run out of cash,” is incorrect because it is in the active voice, while the original sentence is in the passive voice.
In conclusion, the correct answer is A. Some of them imagined that they would inevitably run out of cash.