Given triangle abc, what is the first step in proving that the three medians intersect at the same point? construct midpoint d on segment ab construct point d anywhere outside triangle abc construct line de parallel to side ab construct point d anywhere inside triangle abc

We need to prove that the three medians intersect at the same point.

The 3 medians of a triangle meet at the same point. This point is called the centroid of the triangle
The median is the line that join a vertex of the triangle and the midpoint of the side opposite that vertex.

So, we need to construct the midpoints of all the three sides 
so, it is logic to begin to construct the midpoint of one of the sides.

By configuring the given options, so the correct option is the first
Construct midpoint D on segment AB