Select the option that is related to the third word in the same way as the second word is related to the first word.
Videographer : Camera : : Doctor : ?

A Videographer uses a Camera as their primary tool or instrument to perform their work. Similarly, a Doctor uses a Stethoscope as a primary diagnostic tool to examine patients.
Vimeo
+ 1

Hence, 'Stethoscope' is the related word.