It's sunny.

A, because the latitude of Lianshui is not 0, it can't always be equal to day and night, so it doesn't meet the meaning of the question;

B, according to the picture analysis, at this time, the sun shines directly in the southern hemisphere, and the days in the northern hemisphere are short and the nights are long, which does not meet the meaning of the question;

C, according to the analysis in the figure, at this time, the sun is directly near the equator in the southern hemisphere and is moving northward, so the days in the northern hemisphere are longer and the nights are shorter, so it is correct;

D. According to the picture analysis, at this time, the direct point of the sun moves northward, so the days in the northern hemisphere gradually become longer and the nights gradually become shorter, which is not in line with the meaning of the question.

So choose: C.