Which of the following sentences is grammatically wrong？

Which of the following sentences is grammatically wrong？
A.If I was a bird， I would fly in the blue sky.
B.
If Tom worked harder， he would have succeeded in passing the exam.
C.I would offer you help if I were there.
D.If you were in such a situation， what would you do？
正确答案：If I was a bird， I would fly in the blue sky.