What does an equinox signify

What does an equinox signify
A: The shortest day
B: The longest day
C: Equal duration of day and night
D: None of these

An equinox occurs when the sun is over the equator. Day and night are nearly equal worldwide. It marks the starts of spring and autumn in the astronomical calendar. Many cultures align planting rituals and festivals with these moments due to predictable seasonal light and temperature shifts.