A:spring
B:summer
C:autumn
画出下图中小旗绕O点顺时针旋转90度后的图形。
Progress suggests a person's ability to change the way he is living at the moment and it must ______ a better life and a better way of doing things.
某学校的生物课外小组开展大白菜丰产实验,每棵重约4Kg。请问大白菜增产的物质主要来自 ( )