Which solar term is the length of day and night?

The first step is to examine geographical knowledge.

The second step, China in the northern hemisphere, the variation law of the length of day and night in the northern hemisphere: the days are long and the nights are short in summer (March 2 1-September 23), and the days are short and the nights are long in winter (September 23-March 21day), and the vernal equinox and autumn are equally divided. Item D, "Hard solitary flowers break the slight cold, and the flower heart should be like a guest's sorrow", comes from Mu Furong in front of the window by Fan Chengda, a poet in the Southern Song Dynasty. The "slight cold" in the poem is 23 solar terms, ranging from 65438 to1October 5-7, so the days are short and the nights are long.

Therefore, choose the d option.