Down’s cephalometric analysis of a patient reveals a high mandibular plane angle. Which of the following landmarks are used for the construction of the mandibular plane in this analysis?: (A) Go-Me, (B) Go-Gn, (C) Tangent to the lower most border of the mandible, (D) Me-antegonial notch
Answer is A. Tweed and Ricketts- straight line tangent to the lower most border of the mandible.
Downs- line joining Gonion to menton.
Steiner- line joining Gonion to gnathion.
Bimler’s line- line joining menton to antegonial notch.

Ref: Radiographic cephalometry:Jacobson A