"I am a man" should be accepted as a correct answer, since it is equivalent to "I am human" in one of its meanings. (Even though it may not be "politically correct" to use these days.) I really like this course and don't mind typing in "I am a human" :) In regard to "I am a human" vs. "I'm human" - Both exist, but there is a slight difference in the meaning and situations when they would be used. Examples: I am sorry for the mistake. I'm human. vs. Here on Babylon 5, I'm not so special, since I am a human. There are many humans here.
In English you would say "I'm human" not "I'm a human". There is a limit to literal translation!
"Human" is mainly an adjective, but can be used as a shortcut noun to signify "human being". Hence the correct translation would be "I am a human being" or "I am a human person". When the nuon is removed, translating literally as "I am A human" sounds odd in English (except maybe in science fiction). So "I am human" should be accepted as an idiomatically equivalent translation.