A:go swim
B:go to swimming
C:go swimming
D:going swimming
— Your painting really improves a lot.
— I have taken a painting ________ since last year. I find my painting is getting better.
人类祖先与猿分界的重要标志是( )
材料一:东北地区≥10 ℃积温和粮食作物(图中阴影)分布图。
材料二:东北地区和长江三角洲地区人均耕地面积(图乙)和谷物单产(图丙)比较。
材料三:东北地区是我国重要的工业基地,良好的工业基础为农业发展提供了机械设备、化肥等生产资料。
家庭联产承包责任制之所以能在全国普遍推进,根本原因是