The correct answer is D. Western depressions.
The winter rainfall in Chhattisgarh area is mainly due to western disturbances. These are extratropical storms that form over the Mediterranean Sea and move eastwards across the Indian subcontinent. They are caused by the interaction of the cold air from the Mediterranean Sea and the warm air from the Indian Ocean.
Western disturbances are most common during the winter months, when the temperature difference between the two air masses is greatest. They bring rain and snow to the northern and western parts of India, including Chhattisgarh.
The other options are incorrect. The retreating monsoon is a seasonal wind that blows from the southwest to the northeast during the summer months. It does not bring rain to Chhattisgarh. The southwest monsoon is the main source of rainfall in India.
The southeast monsoon is a seasonal wind that blows from the southeast to the northwest during the summer months. It does not bring rain to Chhattisgarh. The southeast monsoon is a secondary source of rainfall in India.
The southwest monsoon is the main source of rainfall in India, while the southeast monsoon is a secondary source. The retreating monsoon does not bring rain to Chhattisgarh.