ANS:D - all a, b & c

1. \Stabilization: Promoters can stabilize the catalyst by helping maintain its structure and preventing it from undergoing changes or degradation during the reaction process. This stabilization ensures that the catalyst remains active and efficient over extended periods of use.
2. Increasing Effectiveness: Promoters can enhance the catalytic activity of the catalyst, making it more effective in promoting the desired chemical reactions. They can do this by optimizing the surface area available for reaction, facilitating the adsorption of reactant molecules, or promoting specific reaction pathways.
3. Improving Strength & Heat Resistance: Some promoters can improve the mechanical strength and thermal stability of the catalyst. This improvement is crucial for withstanding the harsh conditions often encountered in industrial processes, such as high temperatures and pressures. Additionally, enhanced heat resistance can prevent catalyst deactivation due to thermal degradation.

Therefore, the presence of a promoter along with the catalyst serves multiple purposes, including stabilizing the catalyst, increasing its effectiveness in promoting reactions, and improving its strength and heat resistance. Hence, the correct option is: all a, b & c