Air pollution has become ______ than ever before. We must do something to stop it.
A:serious
B:more serious
C:most serious
D:the most serious
①80℃时,甲物质的溶解度是____;
②t2℃时,把甲、乙、丙三种物质的饱和溶液降温到t1℃,溶质质量分数不变的是____;
③若要让乙物质从它的饱和溶液中全部结晶析出,应采取的方法是____.