3)
a) incenter
b) angle bisectors
c) the incenter is equidistant from the sides of the triangle
d) ???
2)
a) orthocenter
b) altitudes
c) the distance from the vertex to to the orthocenter is two-thirds the length of the altitude
d) ???
1)
a) circumcenter
b) perpendicular bisectors
c) the circumcenter is equidistant from the vertices of the triangle
d) ???