I'm not sure where you read "by" was an adverb.
It's a preposition.

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Given this sentence:
The ball was kicked by Jim.
I read that "by" is NOT a preposition in this sentence. Instead it is a adverb.
Is this because it is a passive sentence?
If the sentence was this:
Jim kicked the ball by the car.
Is "by" a preposition because the sentence is a active sentence?
Is a sentence always passive by the existance of a auxiliary verb?
I'm not sure where you read "by" was an adverb.
It's a preposition.
Here is the link were it says it is a adverb and explains why it is:
http://www.csun.edu/~galasso/completehandbook4.htm
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