(A) 23rd February and 21st September
(B) 21st March and 23rd September
(C) 23rd March and 21st September
(D) 28th June and 26th December
The answer is: (B) 21st March and 23rd September
When the Sun is exactly above the Equator, it makes day and night of equal length. This event is called equinox and the two equinoxes occur in March (about 21st March) and September (about 23rd September).