An excellent breakdown of the linguistic and grammatical differences between the passive and active voice and the similar but distinct simple and continuous aspect. Not something I've ever truly grasped myself; also some nice tips on writing i.e. don't just avoid the passive voice, understand why and use it appropriately.

An easy test for whether or not you’re dealing with a passive voice construction is whether you can add “by zombies” and the sentence makes sense. “I was robbed by zombies!” “Have you ever been kissed by zombies?” “Our country is built on laws…erm, by zombies.”