The correct answer is option 4, which states that all three options 1, 2, and 3 have taken place in recent years.

Option 1 refers to gauge conversion, which is the process of changing the width between the rails of a railway track to accommodate trains of a different gauge. This is done to improve connectivity and allow for the smooth movement of trains across different regions.

Option 2 refers to track electrification, which involves the installation of overhead electrical lines to power trains instead of relying on diesel engines. This helps in reducing greenhouse gas emissions and is more economical in the long run.

Option 3 refers to the implementation of automatic signals, which are used to control the movement of trains, ensuring safety and efficiency. Automatic signals use sensors and computer systems to detect the position of trains and regulate their speed and movements.

In recent years, the Indian Railways has been focusing on these qualitative improvements to enhance the overall efficiency, safety, and sustainability of its operations.