题目

把一本物理书放在水平桌面上静止不动，下列各对力中属于平衡力的是 A．书对地球的引力和地球对书的引力 B．书受到的重力和桌面对书的支持力 C．书对桌面的压力和书受到的重力 D．书对桌面的压力和桌面对书的支持力 答案：BKangkang is a Chinese boy. He is a student. He is 14. Kangkang likes to make friends(交朋友). Now he receives(收到) a letter from Sam, his pen pal in England. The letter is in English. Sam is a student, too. He likes China. He wants to visit the Great Wall.1.Kangkang is a _________.A. teacher B. student C. doctor2.The letter is in _________.A. Chinese B. Japanese C. English3.Sam lives in _________.A. China B. the U.S.A. C. England4._________ wants to visit the Great Wall.A. SamB. KangkangC. Kangkang’s brother5.Sam is Kangkang’s _________.A. classmate B. pen pal C. teacher