option D) Zero
Because 4 - 3 = 1 which means that if you superimpose the segment of 4 units over the segment of 3 units, the difference is 1 unit. And then, if you raise one of the sides just a tiny angle, the distance between the ends of both segments is greater than one. That means that you need a segment larger than 1 unit to join the edges of segments 4 and 3, and so form a triangle.