The next step is Use a compass to draw a circle centered at B that is half the length of AB. Option B
Given a circle having center A, and radius equal to AB.
One side of equilateral Triangle = AB
We have to draw two sides which have length equal to AB.
Draw a circle having center B and radius equal to AB.
The Circle will pass through center A and cuts the Original circle at P.
Join AP and BP.
This is the equilateral triangle that we are interested in.
The complete question
What is the next step in the construction of an equilateral triangle
a. Use a compass to draw a circle centered at A with a radius that is half the length of AB
b. Use a compass to draw a circle centered at B that is half the length of AB
c. Use a straightedge to draw a line passing through B that is perpendicular to AB