Voice distribution

Hello everyone

I am attaching a file from Piston's harmony book, because I cannot understand how the voices are distributed.

For example: in the chord of the first measure, there is an A in the bass, an E in the tenor, a C in the alto, and an E in the soprano.

In the third measure (first chord), I ask you: how do you think the voices are distributed? And in the chord of the second measure?

Thanks to everyone