
21.When did the Chinese begin to use natural ice to keep food fresh?
A.The Zhou Dynasty.
B.The Pre-Qin Dynasty.
C.The Ming Dynasty.
D.The Qing Dynasty.
22.Which of the following has the same function as the refrigerator today?
A.Icehouse.
B.Ice container.
C.Bed-mat.
D.Porcelain pillow.