The fourth roots of 1 are 1, -1, i and -i. We can check this easily. So the correct picture is C (all roots lie at the axis with the coodinates of ±1).

Now, fill out the empty fields at a top of the question. The 1 as a complex number has an angle of 0. So,

the roots are: cos([0 + (2π)*k]/4) + i*sin([0 + (2π)*k]/4), k = 0,1,2,3. (4 pcs)

2π/4 = π/2 = 90° (/4 is from the fourth degree). So,