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    There are many apple trees in a garden. They're good friends. One day an old tree is ill. There are many pests in the tree. Leaves of the tree turn yellow. The old tree feels very sad and unwell. Other trees send for a doctor for him. At first, they send for a pigeon, but she has no idea about it. Then they send for an oriole(黄鹂), and she can't treat the old tree well either. Then they send for a woodpecker. She is a good doctor. She pecks a hole in the tree and eats lots of pests. At last the old tree becomes better and better. Leaves turn green and green.

我市商河境内有许多温泉，经检测分析，该温泉属于硅酸盐温泉，对心脏、高血压等有良好的医疗保健作用。已知硅酸盐中硅元素的化合价为+4价，则硅酸的化学式为