Answer: Choice C
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Step-by-step explanation:
Notice how, for each table shown, the x values are all increasing when reading from left to right.
To have a negative slope, the y values must decrease when reading from left to right.
Table C shows this. Eg: going from y = 8 to y = 0.
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We can pick two points from table C and plug them into the slope formula.
I'll pick the first two columns for the (x,y) values.

You should get a slope of -4 for any pair of columns you pick in table C.
Tables A, B and D will produce some positive slope value.