The maximum possible heat transfer between the two fluids

Question

For a heat exchanger, DT_max is the maximum temperature difference and DT_min is the minimum temperature difference between the two fluids. LMTD is the log mean temperature difference. C_min and C_max are the minimum and the maximum heat capacity rates. The maximum possible heat transfer (Q_max ) between the two fluids is                                                  

      (a) C_minLMTX                                                     (b) C_minDT_max

      (c) C_max DT_max                                                     (d) C_max DT_max