A human being is an intelligent creature, ............?
a) isn't it wrong except isn't it [the fact]
b) isn't he possible
c) isn't she possible
d) aren't they possible
e) aren't we not excluded but better take it as being wrong
The basic trick in deciding which one is correct is in the fact that a human being defines a type of beings. In the context it is possible to give a more precise definition of this type and based on that to define which one is preferable.
A human being = all human beings (they) = a typical member of the group of human beings (he or she depending what typical means for you)
A human being is an intelligent creature, isn't he? Normal and formal
A human being is an intelligent creature, isn't she? Possible, but maybe funny, you are saying actually that you are regarding women as the only being smart among human beings, which is not impossible at all
A human being is an intelligent creature, aren't they? Acceptable, but within the broader context
Observe this
- A nuclear scientist is an intelligent creature, isn't he? The one who is a nuclear scientist must be clever.
- A nuclear scientist is an intelligent creature, isn't she? The one who is a woman and a nuclear scientist must be clever.
- A nuclear scientist is an intelligent creature, aren't they? All nuclear scientists are clever.
With he and they you encompass both he and she, with she you specify women only. We is possible only within the context; in my example, it could mean only a small group of human beings, those whose action shows how human kind is smart or capable.
We have finished this marvelous movie. What a movie that is! It won 12 Oscars. A human being is an intelligent creature, aren't we?