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A．Rainwater dissolves materials as it comes down a base of limestone or shale.
B．People put dissolved materials into the soft water.
C．People treated hard water with special medicine.
D．Rainwater mixed with seawater.
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单项选择题A．On how to give presents to others on Christmas.B．On how to spend time with grandparents.C．On how to play hide-and-seek.D．On how to celebrate Christmas.

A．On how to give presents to others on Christmas.
B．On how to spend time with grandparents.
C．On how to play hide-and-seek.
D．On how to celebrate Christmas.

单项选择题A．At a music store.B．At the post office.C．In a German class.D．On the Internet.

A．At a music store.
B．At the post office.
C．In a German class.
D．On the Internet.