A:①②
B:②③
C:②④
D:①④
①大道之行,天下为公 ②己欲立而立人,己欲达而达人
③知人者智,自知者明 ④先天下之忧而忧,后天下之乐而乐
—What do you often do _______ classes to relax yourselves?
— We often chat together, do eye exercises or do some running around the school.
下列粒子结构示意图中,表示阳离子的是( )