Described below are the first three steps for constructing the perpendicular bisector of a line segment.
1. Start with a line PQ.
2. Place the compasses on one end of the line segment.
3. Set the compasses' width and draw an arc above and below the line.

What is the exact width required in step 3?

A) one-half the line
B) one-third the line
C) two-thirds the line
D) no exact width required