前运算阶段的显著特点是（）。
A.感觉和动作的分化
B.思维的可逆性
C.语言的飞速发展
D.思维开始萌芽
参考答案：C
“Youth” is regarded by many people as a time in their life _____ fun, passion, and imagination seem limitless.
A．that
B．which
C．when
D．where
内燃叉车运动时机油比静止时机油面（）。
