When does 'Viṣuva-dina' (Equinox day, when day and night are equal) occur according to the 'Sāyaṇa' (tropical) system of Indian Astronomy?
A. Sāyaṇa Mēṣa Saṃkrānti (Sun enters tropical Aries)
B. Sāyaṇa Karka Saṃkrānti (Sun enters tropical Cancer)
C. Sāyaṇa Tulā Saṃkrānti (Sun enters tropical Libra)
D. Sāyaṇa Makara Saṃkrānti (Sun enters tropical Capricorn)
E. Sāyaṇa Kanyā Saṃkrānti (Sun enters tropical Virgo)