A reaction is spontaneous when the Gibbs free energy change (ΔG) is negative. This is determined by the equation ΔG = ΔH - TΔS, where ΔH is the enthalpy change, T is the temperature, and ΔS is the entropy change. Therefore, a reaction is spontaneous if ΔH is negative and TΔS is negative, or if ΔH is positive and TΔS is positive and greater than ΔH. In other words, for a reaction to be spontaneous, the decrease in enthalpy (ΔH) must be greater than the increase in entropy (TΔS). 

In summary: For a reaction to be spontaneous, either ΔH must be negative (exothermic) and TΔS must be smaller than ΔH, or TΔS must be positive and larger than ΔH. The key is to ensure that the decrease in Gibbs free energy (ΔG < 0) is negative. 

Applying values to those parameters, options A, B and C appear correct because they'll all make ΔG negative but the one that will mostly enhance spontaneity is option A because ΔG = -ve, ΔH = - ve.