Choice "D" is correct. When a partner's share of partnership liabilities increases, that partner's basis in the partnership increases by his share of the increase. Since the partner has unlimited liability, the partnership liabilities are treated as if the partner personally borrowed the money and then contributed it to the partnership.Choice "b" is incorrect. It increases, not decreases, the partner's basis by his share of the increase in the liabilities.Choice "a" is incorrect. It increases, not decreases, the partner's basis by his share of the increase in the liabilities.Choice "c" is incorrect. The partner's basis is affected; it increases by the partner's share of the increase in liabilities.