测得Fe和Fe2O3的混合物中氧的质量分数为15%，则单质铁的质量分数为请选择ABCD6Q2a;?*M-Y']*|7c5y(A/f8v4[-d:\4c9H+X*|
A. 30%-Y']*|7c5y(A/f8v4[-d:\4c9H+X*|
B. 50%-Y']*|7c5y(A/f8v4[-d:\4c9H+X*|
C. 70%-Y']*|7c5y(A/f8v4[-d:\4c9H+X*|
D. 85%-Y']*|7c5y(A/f8v4[-d:\4c9H+X*|