It's not proper for kids to have too much pocket money because they may buy ______.
A:something necessary
B:necessary anything
C:something unnecessary
D:unnecessary something
(2015•泰安)如图,⊙O是△ABC的外接圆,∠B=60°,⊙O的半径为4,则AC的长等于( )
关于亚洲的地理特征,错误的是( )
用电石(主要成分为CaC2)与水反应可制取乙炔,最终还可得到电石渣.某电石渣中含氢氧化钙92.5%,其余为杂质,此电石渣可用于处理电镀厂排出的酸性废水.请完成: