a. They threw me in a cage like an animal.
Is just fine. Brief, to the point, not a lot of room for the reader to get the wrong message.
The others are still OK, but progressively less to the point.
Even though there is potential for confusion of intent, the overall imagery is simple enough to grasp at first read. Whether the reader considers the throwing to be animalistic or the act of caging is actually a bonus - you can mean both without hurting the sentence. Two for the price of one, you are conveying meaning about the captors & captive.
The sentence reads so naturally, that you would only hesitate if it had a 'surprise' ending...
They threw me in a cage like a box.
Now we're describing the cage, rather than how a postal worker would handle a package.
The original sentence is clear enough to avoid this type of mis-communication.