Cooperation or teamwork, the importance of which is often _____, plays an important part in

football matches.    [ ]

A. stressed  

B. counted  

C. paid attention to  

D. talked

依据皮亚杰的发生认识论，处于前运算阶段的儿童的思维特点是( )。

A．具体性

B．不可逆性

C．自我中心主义

D．守恒性