It was really the correct answer

As I was looking at Nathan's school papers last night, I saw an answer that was marked wrong that I felt should have been marked correctly.  They had just read a story about space, who the first woman was in space and the work she does with robots.  The test was over the story.  The question that Nathan got wrong (at least according to his teacher and not his Mom) was,

A robot is a __________ that does a lot of hard work.

There was something like six fill-in the blank questions with six possible choices at the top.  My smart son filled in the blank with the word "woman"  and it was marked wrong.  He was supposed to put "machine" in the blank, but I still think he got it right!