The best answer is B, but not for tax purposes. B is the correct answer in order to be fair to the partners. Let's say that A and B form a partnership and A contributes $100,000 and B contributes land and building which she bought for $60,000 and on which $10,000 of depreciation has been recorded. B's cost is $60,000, her book value of the property is $50,000, but the fair value of the property is $100,000.
If the partnership accepts the property at its fair value, A and B will have equal shares of the partnership. If they record it at B's book value, B would contribute assets with a fair value of $100,000 but would wind up with only 1/3 ownership of the partnership. That would be unfair to B because it would transfer part of the fair value of the asset to A.
However, the partnership would have to continue depreciating the original cost of the property for tax purposes.