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Can I say,

(a) An ostrich is a bird that / which cannot fly.

(b) An ostrich is a kind of bird but cannot fly.

(c) The ostrich is a bird but it cannot fly.

(d) The ostrich is a bird but cannot fly.

(e) The ostrich is a bird but it is unable to fly.
Comments  
I would use the definite article, something I've learned from this forum.
How about the sentences? All correct?
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As I said, only those with 'the' are grammatically correct.
So, I try:

(a) The ostrich is a bird that / which cannot fly.

(b) The ostrich is a kind of bird but cannot fly.

(c) The ostrich is a bird but it cannot fly.

(d) The ostrich is a bird but cannot fly.

(e) The ostrich is a bird but it is unable to fly.

All correct?