①客观的物质性活动
②主观的社会性活动
③改造世界的一切活动
④有意识有目的的活动
A:①②
B:②④
C:①④
D:①③
— Mum, can you give me some advice on how to behave myself at the table?
— Well, I do have some advice. , please keep quiet while eating.
解方程.
决定地球表面南北回归线最北、最南界线位置的是( )
17-9=( )