The important part for answering this question is: The stapes or stirrup is a bone in the middle ear of humans and other mammals which is involved in the conduction of sound vibrations to the inner ear.
This justifies what answer for what question? Q & A:
Passage: The stapes or stirrup is a bone in the middle ear of humans and other mammals which is involved in the conduction of sound vibrations to the inner ear. The stirrup-shaped small bone is on and transmits these to the oval window, medially. The stapes is the smallest and lightest named bone in the human body, and is so-called because of its resemblance to a stirrup (Latin: Stapes).

Question: Based on this passage, where can we find the smallest bone in the human body?
in the middle ear