A
x y
1 1
2 4
3 9
4 16
c
x y
1 4
2 2
3 4/3
4 1
b
x y
1 1/2
2 1
3 3/2
4 2
d
x y
1 3
2 5
3 7
4 9

the tables show four relationships between x and y. in which table is there a negative rate of change?
a) a
b) b
c) c
d) d

I'm not sure if you meant to label the table C instead of B, so... this table:

x y
1 4
2 2
3 4/3
4 1

...shows a negative, or decreasing, rate.

This is because the x-axis usually represents time and we can see that as x (time) increases, y (an amount of something) is getting lower each time.
4 > 2 > 4/3 (1 1/3) > 1