OK! Right section

Anyway, I took up theory not long ago and I'm trying to write a blues melody over the following chord progression:

G7 C7 G7 G7
C7 C7 G7 G7
A-7 D-7 G7 C7

At first it seemed like a simple task, then it hit me.

What key am I supposed to be in? How do I even go about applying a blues scale? I was under the impression I could only play the notes of the given chords, so where do scales come in at all?

Any help at all is greatly appreciated.
i would play something in G over that...i think. but im very tired so i could easily be missing something
well there's always the pentatonics. i'll let someone else write out a blues scale for you
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What I like to do is play the minor pentatonic of each root, over their chords, like this:

G minor pentatonic C minor pentatonic... etc.

In a normal I7 IV7 V7 blues progression, the minor pentatonics essentially combine to make the relative major of the root (which would work out to be Bb major)
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