In this task, you are given a multiple-choice question and you have to pick the correct option. Answer with option indexes (i.e., "A", "B", "C", and "D").

The southern and northern hemisphere's seasons are opposite each other, so when the northern hemisphere is having it's longest day, it's the southern hemisphere's (A) winter solstice (B) fall equinox (C) summer solstice (D) spring equinox
A