The correct answer is: A. June 21
The Earth’s axis is tilted at an angle of 23.5 degrees relative to its orbital plane. This means that the Northern Hemisphere is tilted towards the sun in June and away from the sun in December. The opposite is true for the Southern Hemisphere.
On June 21, the Northern Hemisphere is tilted towards the sun and the Southern Hemisphere is tilted away from the sun. This means that the Northern Hemisphere experiences its longest day and the Southern Hemisphere experiences its shortest day.
On December 22, the Northern Hemisphere is tilted away from the sun and the Southern Hemisphere is tilted towards the sun. This means that the Northern Hemisphere experiences its shortest day and the Southern Hemisphere experiences its longest day.
July 21 and November 22 are not the longest or shortest days in either hemisphere.