Is the sentence bees were left alone to work on their comb active or passive?

The sentence "Bees were left alone to work on their comb" is passive.

Here's why:

* Passive voice focuses on the action being done to the subject. In this case, the bees are the subject, and they are being "left alone" (the action).

* Active voice focuses on the doer of the action. We don't know who left the bees alone, so the sentence can't be active.

To make the sentence active, we would need to know who left the bees alone, for example:

* "The beekeeper left the bees alone to work on their comb."