As shown in the figure, it is a schematic diagram of the change of sun height at noon in Xi 'an during the vernal equinox, summer solstice and winter solstice (solar terms in the northern hemisphere).

As shown in the figure, it is a schematic diagram of the change of sun height at noon in Xi 'an during the vernal equinox, summer solstice and winter solstice (solar terms in the northern hemisphere). The following sequence is consistent with the figure ( Xi 'an is located in the north of the Tropic of Cancer, so in a year, the noon sun height is the highest in summer solstice, the lowest in winter solstice, and the noon sun height in vernal equinox and autumnal equinox is between the maximum and minimum, so it can be judged as ① summer solstice, ② vernal equinox and ③ winter solstice.

So choose: B.