23．________，so the Egyptians invented balls instead．

A． Throwing stones was a popular game for children

B． Stones were．too heavy to throw

C． Stones might hurt children

D． They didn’t have so many stones

[单选题]23．________ is the most popular way of cooking in the USA．A．BakingB．Frying ．C．Boiling

[单选题]以SO42-沉淀Ba2+时，加入适量过量的SO42-可以使Ba2+离子沉淀更完全。这是利用（）A .同离子效应B .酸效应C .配位效应D .异离子效应

[试题]TheancientEgyptiansaresupposed_________rocketstothemoon.A．)tosendB)tobesendingC．)tohavesentD)tohavebeensending

[单选题]24．The Egyptians made the first balls with _________ ．A． animal skinB． something lightC． leaves and vinesD． paper

[单选题]某无色溶液中可能含有①Na+，②Ba2+，③Cl—，④Br-，⑤SO42-，⑥SO中的若干种，依次进行下列实验，且每步所加试剂均过量，观察到的现象如下：下列结论正确的是（）。A . 肯定含有的离子是①④⑤B . 肯定没有的离子是②⑥C . 不能确定的离子是①D . 不能确定的离子是③⑤

[试题]() switching was invented in the late 1960s for data communications.A．Frame B．Link C．Packet D．Line

[单选题]SDLC was invented by IBM to replace the older Bisynchronous protocol for wide area connections between IBM equipment ．A varietion of the (71) protocol called NRM is essentially the same as SDLC．SDLC is (72) protocol like HDLC , Frame. Relay or X．25．A

[单选题]SDLC was invented by IBM to replace the older Bisynchronous protocol for wide area connections between IBM equipment . A varietion of the (71) protocol called NRM is essentially the same as SDLC. SDLC is (72) protocol like HDLC, Frame. Relay or X.25.

[单选题]甲、乙、丙、丁四瓶溶液分别是K2CO3、Ba（NO3）2，H2SO4、K2SO4，中的一种，其中甲分别能C与乙、丙、丁发生反应，甲应该是（）。A . K2SO4B . H2SO4C . Ba（NO3）2D . K2CO3

[单选题]A．Man invented a lot of sports equipment． The first true piece was the ball．Thousands of years ago，in Egypt，the children's favorite game was throwing stones． But a badly thrown stone could hurt a child． Looking for something less dangerous to throw，