Another Third Form Lesson 5 question

[amyco]

I am afraid we are coming upon the time when we are going to have many more questions!

Specifically, Lesson 5 Worksheet 6, IV Translation, no. 2.

And so, food has not been given to the people.

The answer is given as "Itaque cibus populi datus non est."

We are not sure why it is "populi" and not "ad populum." Our reasoning: "populi" is either dative or ablative. It can't be dative because you can't have an indirect object with the passive voice (can you?). We don't think it could be ablative, because it isn't ablative of agent which would be "by the people." And so we think it should have a preposition.

Thanks for any help and explanation!

Amy