In choice A, x = 2 repeats. In other words, x = 2 leads to multiple y outputs. So this is not a function. Choices B and D are similar stories. A function is only possible if every x leads to exactly one y value only. The graph must pass the vertical line test.
Side note: the y values can repeat, but the function won't be one-to-one.
1) 1ml % 6 marbles = about 0.17ml so the volume per marble is 0.17ml 2) 10-(0.17x4) = 9.32 so that is the original volume 3) then 9.32 + (0.17 x 13) = 11.53ml 4) it is linear because for every marble placed inside the cylinder the volume increases by about 0.17ml the slope means amount of marbles placed vs. volume in cylinder
