The nodal points in a coaxial spherical optical system can be defined as following.

pair of conjugate points on the optical axis which have a transverse magnification of unity.A pair of conjugate points on the optical axis which have a relative angular magnification of unity.
C、 A pair of conjugate points on the optical axis which have a longitude magnification of unity.
D、The conjugate points corresponding to the axial object points at infinity.