[例1] Strange things were happening in the countryside of northeast Hebei.(主旨句) For three days the water in the village wells rose and fell, rose and fell.Farmers noticed that the well walls had deep cracks in them.A smelly gas came out of the cracks.(支持句1) In the farmyards, the chickens and even the pigs were too nervous to eat.Mice ran out of the fields looking for places to hide.Fish jumped out of their bowls and ponds.(支持句2) At about 3：00 am on July 28, 1976, some people saw bright lights in the sky.The sound of planes could be heard outside the city of Tangshan even when no planes were in the sky.(支持句3) In the city, the water pipes in some buildings cracked and burst.(支持句4) But the one million people of the city, who thought little of these events, were asleep as usual that night.
[分析] 本段的第一句为段落主旨句，后面的句子组成了支持句群，详细说明了“Strange things”的具体内容。
