**Explanation:**

The South-West monsoon is a significant weather phenomenon in India that brings the majority of the country's rainfall during a particular period of the year. The monsoon season in India typically lasts from June to September and is characterized by the arrival of moisture-laden winds from the Arabian Sea and the Bay of Bengal.

**Contribution of South-West monsoon to India's rainfall:**

The South-West monsoon is responsible for a significant portion of India's total rainfall. The correct answer to the question is option 'A', which states that the South-West monsoon contributes to India's total rainfall up to the extent of 80-90%.

**Factors supporting the answer:**

1. **Rainfall distribution:** The South-West monsoon is the primary rainy season in most parts of India, accounting for the bulk of the annual precipitation. It brings rainfall to various regions, including the west coast, central India, and the northern plains.

2. **Magnitude and duration:** The South-West monsoon is characterized by its magnitude and longevity. It typically covers a vast geographical area and lasts for several months. The prolonged duration and widespread coverage result in a significant contribution to India's overall rainfall.

3. **Dependence of agriculture:** India's agriculture is predominantly rainfed, and the success of crops depends heavily on the monsoon rainfall. The South-West monsoon plays a crucial role in providing water for agricultural activities, making it a vital factor in the country's food production.

4. **Monsoon forecasting:** The Indian Meteorological Department (IMD) extensively monitors and forecasts the South-West monsoon. The accuracy of these forecasts is essential for various sectors, including agriculture, water resource management, and disaster preparedness, highlighting the importance of the monsoon's contribution to India's rainfall.

5. **Rainfall statistics:** Historical rainfall data confirms the significant contribution of the South-West monsoon to India's total rainfall. Over the years, it has been observed that a substantial portion of the country's annual precipitation occurs during the monsoon season.

In conclusion, the South-West monsoon contributes to India's total rainfall up to the extent of 80-90%. This is supported by the distribution, magnitude, duration, agricultural dependence, monsoon forecasting, and historical rainfall statistics.