In the Mapping of Venus by the Orbiting Magellan Spacecraft

In the mapping of Venus by the orbiting Magellan spacecraft, what parameter was measured by the sensors in order to produce three-dimensional maps of the planet's surface?

A) precise photographs of the extreme limb of the planet, taken at UV wavelengths to which the atmosphere is transparent, that showed detailed profiles of the planet's surface
B) time delay of the return of reflected radio waves
C) wavelength and hence Doppler shift of reflected radio waves
D) pairs of photographs taken from different angles that were then combined stereoscopically to produce contour maps