The answer is the option in the spoiler, but I can't quite figure out why.
D (bottom left)
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I'm not a fan of these types of puzzles but I think the reasoning is as follows
Rotate the central diamond image $45^o$ anti-clockwise so that their edges are now horizontal and vertical.
Then, in each row, if we take the XOR value of the edges surrounding the left square with the edges surrounding the middle square, we obtain the edges surrounding the right square.
In particular, on the bottom row, the left square has got an edge on its right-hand side and the middle square will have edges on its top and left. The result of taking the XOR of these edge values is a square with edges on its top, left and right. This is the image in the bottom left of the possible answers.
The answer may be:
In the first two examples, the state of the bottom line is the same between the shaded box at left and the unshaded box at right. the middle symbol is an arrow, pointing to a direction. In the middle symbol, the two exterior lines can be interpreted as an arrow, which points the direction in which the other exterior line should move. In the final example, the lack of bottom line under the shaded square indicates we should not have a bottom line, and the arrow in the middle square points up, indicating there should be a top line. This corresponds to the figure above.