Imagine the orange cells of grid A are heavy blocks. Grid B shows what happens to them. Which grid shows the same thing happening to C?

In B every orange block has dropped straight down its own column until it rests on the bottom or on another block: the left and middle columns have one block each and the right column has two. In C the left column has 2 blocks, the middle column 2 and the right column 1, so after falling they fill the bottom of each column in those numbers: (a). (b) lets the blocks slide to the left, (c) lifts them to the top and (d) turns the grid.