The arrow looks at the front of the solid, so we draw the front elevation.
The solid is a low base slab with a tall wall at the left (running from front to back) and a tall block at the back right; both are equally high. Between them the slab top is open, so nothing is seen in the gap above the slab.
The left wall and the front of the slab lie in one plane, so the left wall and the slab form one L-shaped outline with no line between them. The right block starts a little beyond the middle and runs to the right end of the slab; its left edge ends on the slab line.
At the front right, the slab is set back, so the end of the slab appears as a small separate rectangle at the bottom right.
Option (1) fills the gap between the wall and the block, option (2) draws the wall lower than the block and separates it from the slab, and option (3) draws the block edge right down through the slab. Option (4) shows the equal heights, the open gap, the merged wall and slab and the small rectangle at the right.
Answer: (4) the fourth answer figure