#### Answer

d d d
d d _
_ _ _

#### Work Step by Step

The 1st, 2nd, and 3rd picture have 2, 3 and 4 letters correspondingly, therefore, it only makes sense for the 4th picture to have 5 letters.
The 1st, 2nd, and 3rd picture have the letters a, b, and c as their letter, therefore, it only makes sense for the 4th picture to have the letter d.
The letters fill the 3x3 grid starting from the top-left square, and filling the first row to the right before moving onto the second row, starting again from the right.
Therefore, we can assume the answer would look like the provided picture.