A:The harder, the better
B:the more hard, the more better
C:The harder, a better
D:more hard, more better
如图所示为某草原生态系统的食物网,据图回答问题:
①用滤纸过滤 ②用分液漏斗分液 ③加热蒸发 ④加入热的饱和食盐水.