Which of the following is TRUE regarding the real interest rate? I. The real interest rate is the opportunity cost of borrowed funds. II. The real interest rate equals the nominal interest rate adjusted for inflation. (关于实际利率的以下哪项是真的？一，实际利率是借款资金的机会成本。 II 。实际利率等于通货膨胀调整的名义利率。——中文由在线翻译而来，仅供参考)
选项：

A: I
B: IIII
C: both I and III和II
D: neither I nor III也不是二