What is the value of one sided lower cusum?

• A. (C_i^-=min u2061[0,x_i-( _0+K)+C_{i-1}^-] )
• B. (C_i^-=max u2061[0,x_i-( _0+K)+C_{i-1}^-] )
• C. (C_i^-=min u2061[0,( _0-K)-x_i+C_{i-1}^-] )
• D. (C_i^-=max u2061[0,( _0-K)-x_i+C_{i-1}^-] )