资料题：What is the longest day of the year（　）。

The year is divided into four seasons, known as spring, summer, fall, and winter.Each season is about three months long.In most places the earth is warm in spring and summer and cooler in fall and winter.Spring comes as our part of the earth begins to tip more towards the sun.This happens about March 21.At this time our nights last about twelve hours.Our days last the same time.In most places buds and leaves appear on the bare trees, and flowers begin to burst into bloom.Summer begins about June 21, the longest day of the year.This is when our pert of the earth is tipped the most toward the sun.The sum's hot beams fall steadily down.Leaves cover the branches of trees thickly.Insects buzz around brightly-colored flowers.The sun appears high in the sky.In fall the weather begins to get cooler.Starting about September 21, our part of the earthbegins to tip away from the sun.Days and nights are almost the same length.In most places theleaves on the trees begin to tum from green to beautiful reds, oranges, yellows, and browns.Winter begins about the twenty-first of December.This is the shortest day of the year.As our part of the world tips far away from the Bun, the sun's beams no longer come directly down on us.In most places the days grow cold, north winds blow, and snow often falls.Plants die or rest for a while.