已知集合U={1,4,7,8,9},A={4,7,9},则CUA=______.
∵U={1,4,7,8,9},
A={4,7,9},
∴CUA={1,8}
— Why does the lake smell terrible?
— Because large quantities of water _________.[ ]
A. have been polluted
B. has polluted
C. have polluted
D. has been polluted
某兴趣小组需要用足量的10%稀盐酸与下列四种物质反应,制取通常状况下500mL的CO2气体,选择上述四种物质做原料时,称取固体质量最多的是( )
A.小苏打(NaHCO3)
B.纯碱(Na2CO3)
C.碳酸钙
D.草木灰(主要成分是K2CO3)