Answer:
I think A. They occur when the Sun reaches its highest or lowest point in the sky.
Explanation:
The summer solstice is when the sun is Highest in the sky, and the Winter solstice is when the sun is lowest in the sky.
The flow of the Chang Jiang is some 20 times greater than that of the
Huang He. As much of 40% of China's total grain production, 70% of rice
output, and more than 40% of the population are associated with the
Chang Jiang's vast basin that includes more than 3,000 tributaries. With
its numerous tributaries, the Chang Jiang drains nearly 20% of China's
total area. Its upper reaches tap the uplands of the Tibetan Plateau
before sweeping across the enormous and agriculturally productive
Sichuan Basin that supports nearly 10% of China's total population. It
is in the middle course of the Chang Jiang that the controversial Three
Gorges Dam is being constructed.
The answers are B and also C.
