What logically could have gone wrong?

The steps of drawing a circumscribed circle are the following:

1) Draw the 3 perpendicular bisectors of the sides. They all meet at the circumcenter.

Drawing only 2 is enough, since their intersection point is still the circumcenter.

2) We open the compass from the circumcenter to any of the vertices, then we draw the circle.

Among our choices, (b) is not an issue, as explained above.

(c) has to do with drawing the inscribed circle, but nothing to do with the circumscribed circle.

(d) The angle bisectors meet at the center of the inscribed circle. Again, these have nothing to do with the circumscribed circle.

What may have happened, is only (a).

These are the multiples of 15 but what you are probably asking or what are the factors of 15