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　　閱讀理解

　　Lightning is generated when electrical charges separate in rain clouds, though processes are still not fully understood. Typically, positive charges（正電荷） build at the cloud top, while the bottom becomes negatively charged(負電荷的). In most instances of cloud-to-ground lightning, the negatively charged lower portion of the cloud repels negatively charged particles on the ground’s surfaces, making it become positively charged. The positive charge on the ground gathers at elevated points.

　　In most cases of cloud-to-ground lightning, the ground's surface__________.

　　A、is positively charged

　　B、is shifted sideways by strong winds

　　C、is negative charged

　　D、is changed from positively charge to negative charge

　　【正確答案】A

　　【答案解析】本段文字解釋了云層與地面之間的閃電的成因，云層下部帶負電荷，排斥地面表層的負電荷，所以地面表層聚集的是正電荷。答案為A。