A Reference Line Has the Notation "MT6" Under It

A reference line has the notation "MT6" under it. What does this designation mean?

A) The maximum torsion destructive test is performed on 6 inches of the weld on the arrow side of the object.
B) The magnetic particle nondestructive test is performed on 6 inches of the weld on the arrow side of the object.
C) The metal arc welding process is performed on 6 inches of the weld on the arrow side of the object.
D) The machine welding method of the welding process is performed on 6 inches of the weld on the arrow side of the object.
E) none of the above