There are many ____ (different) between living in a big city and living in the countryside.
下列物质中既能跟稀H2SO4反应,又能跟氢氧化钠溶液反应的是( )
①NaHCO3 ②Al2O3 ③Al(OH)3 ④Al ⑤Na2CO3.
溺水时,人体受阻碍的生理活动是( )